Five years ago, long before the Internet became the great marketing innovation of our era, Kevin Sinclair was a disabled computer programmer with a few firm notions.

One was that simplicity was good. Another was that computers were splendid things. A third was that if you registered a certain type of word as your Internet address, people would flock to it as the definitive authority -- the final word.

Out of these ideas, Sinclair paid $40 to secure the right to operate a Web site with the address computer.com. He wanted a business his chronic heart condition would allow him to operate from home, but he adds: "I got it mainly because it was cool. I would have thought it was silly that anyone would ever pay a lot of money for a name."

Sinclair never got around to developing the site. Instead, a couple of weeks ago he sold computer.com to a Massachusetts entrepreneur for $500,000 plus a potentially lucrative chunk of stock.

As the Web has boomed over the past couple of years, entrepreneurs have realized that having an address that sums up a product or category offers a quick leg up.

Mark Pincus, the president of Tioga Systems Inc., a Silicon Valley start-up company that provides direct assistance via the Web to computer users, spent $190,000 earlier this year for the address support.com. "Rather than spend a couple of million dollars trying to convince everyone that some other name, like tioga.com, stood for online support, we thought it was better to buy the name that said it all."

The seller "was a farmer in Iowa," Pincus says. "I wanted to give him the money in cash, but he said he wanted to make a million off the name, so we had to give him stock." If Tioga has a successful public offering, the farmer will get his wish.

Many generic names were originally registered as addresses by fans or hobbyists on little more than a whim. Take Bill Fisher, who works for an Internet start-up in Denver and is mad about beer. "A beer sewer," he cheerfully calls himself, noting that as this interview is progressing, he's drinking a Newcastle drawn from his keg fridge -- basically, a refrigerator that holds 200 glasses of beer on tap.

As an act of homage, in 1993 Fisher registered the names for two of his favorite beers, Guinness and Budweiser. Slightly more difficult was getting permission from Network Solutions Inc., the Herndon company that was then the sole registrar of Internet addresses, to accept something as funky as beer.com. Back then, the Internet was supposed to be serious.

"I had to tell them it was an acronym for Bilfish Energy Exchange Reserve," Fisher recalls.

In 1995, as corporations began to discover the Net, both Budweiser and Guinness came calling for their names. Fisher surrendered them -- he might have been sued for trademark infringement if he hadn't. Budweiser thanked him with 25 cases of brew, while Guinness provided two round-trip tickets to Ireland.

Initially, though, nobody saw the value in beer.com, because it was generic. After all, in the real world, the path to marketing success almost always begins with a distinctive name -- Xerox, say, or McDonald's. The product is then developed around the brand. No one builds a hamburger chain called "Hamburgers."

But the Web doesn't work like the real world. It's organized more like the Yellow Pages. If you're trying to buy a lot of beer for a party, you don't look under "Budweiser," you look under "beer" or "liquor."

Likewise, on the Web, punching in "beer" on a search engine will yield too many sites to get a handle on. Three thousand people a day tried a shortcut by going directly to beer.com -- even though the site was never advertised.

Various entrepreneurs made increasingly attractive offers for the rights to the site. Late last year, Fisher finally made a deal that brought him -- well, to put it in beer terms: "I spent several months in London living with Australians, and you know their appreciation for the finer stuff. Now I can buy all of Australia a round."

Both beer.com and computer.com were bought by the same entrepreneur, Mike Zapolin. "Whoever has the clearest, simplest address, the root name, they've got credibility," says the former vice president at the investment firm Bear Stearns & Co. "There's this amazing opportunity to buy the name of a category from a technical person or hobbyist, put some money in it, and you might be toe to toe with a Fortune 500 company in months."

He redesigned and souped up beer.com, which is equipped with jokes and interactive contests, including a page where fans submit photos of their beer bellies. Zapolin says he currently has offers from several of the big breweries.

Assuming a deal goes through, Fisher -- who retained a third interest in the site -- will become a millionaire. "My only regret is that this didn't happen when I was in college," the 28-year-old says. "I've never had less time to enjoy beer."

For Fisher it was beer; for Alan Miklofsky it was shoes. The co-owner of three stores in Tucson, all called Alan's Shoes, he registered the name shoes.com at the urging of his sister, Kim Bayne.

"I pretty much bullied him into it," says Bayne. "In 1994, I was moderating an e-mail discussion group about marketing on the Net. I started noticing the shorter and simpler the names, the better."

For years, Miklofsky didn't do much with the address. But even with nothing there, it got 2,000 shoe seekers a day from all over the world. In January he began to sell shoes from the site, and he now is mulling over offers from various partners.

"If we had registered alansshoes.com, it would only make sense to the people who already knew who we are," says Miklofsky. "But if you have a generic name, you open yourself up to the possibility of everything in that category."

Such a realization in 1995 would have made him truly wealthy. "If you knew back then, wouldn't you have bought over 200 addresses? But I bought one."

As the Web has increasingly become a place to make a buck, such restraint is no longer widespread. From 1993 through last Dec. 31, Network Solutions had registered 3.3 million addresses. In the six months since then, it has registered 1.8 million more. Many are being bought, at $70 a throw, with the hope of a quick turnaround.

At the most extreme level, there are Web sites set up solely to sell names. A New York company, Cybermultimedia Inc., operates a site with long lists of names for very high prices.

"Insta `anything' sounds great and you know it! Now if you owned www.instawave.com you'd get some serious traffic! Go get 'em Tiger. Here, have the other one's too. What are we gonna do with them anyway," reads a typical overheated Cybermultimedia description, in this case offering the three related sites of instawave.com, instawave.net and instawave.org for a mere $199,999.

Also on offer are questionthedoc.com for $79,000, yourcivilrights.com for $75,000, puertoricanexport.com for $125,000, puertoricanexports.com for $79,000 and washingtoninsider.com for $250,000. Cybermultimedia executives did not return a call asking how many, if any, sites they had sold.

As many as a thousand names are regularly for sale, at much more modest prices, on the auction site eBay.

"When an idea pops into my head I don't grab a note pad to jot it down, I run to my computer to see if it is registered," says Cameron Wilson, a Web designer in Vancouver, B.C., who was recently asking for a minimum bid of $500 for itsaconspiracy.com.

"I registered it after working with someone who is quite a conspiracy theorist," Wilson explains. "Chances are that someone, either a literary figure or a true conspiracy theorist, is going to see this as an intriguing opportunity to have a name that is both memorable and intuitive."

Eventually, maybe, but itsaconspiracy.com didn't sell. In fact, only five out of 38 recent auctions of names on eBay resulted in a transfer of ownership.

The rest either didn't match the minimum price the seller wanted or, like itsaconspiracy.com, didn't receive a single bid. Also in the latter group were outbid.com, for which the owner was asking a minimum of $250, and cutegals.com, for which at least $370 was demanded.

The five domain names that did sell went for modest prices, including ultimatedeals.com for $50 and salesources.com for $69.50. Teenagegirl.com was the day's winner, opening at $1, receiving 13 bids and selling for $1,125.

"I have made a few thousand dollars basically doing nothing but being creative," says the seller, Chuck Ward, a Florida speculator who had three other address auctions running simultaneously on eBay.

While Ward stressed to potential buyers that a site named Teenagegirl.com "could be marketed to companies such as Seventeen magazine, or even the Girl Scouts," in an interview he acknowledges the impetus behind most of the bids.

"It is amazing what money people can make with pornography on the Internet," he says. "Because of moral values and family concerns, I would never do that, but I can sell a product to people that will."

It doesn't surprise Kevin Sinclair that the only really valuable names are the ones that were registered long ago, in innocence.

"The Internet's evolved into something much more complex than it was, so maybe what you need to do to succeed in it is more complex," he says.

He's 42 now, cured of the heart problem that turned him into a stay-at-home dad. But he's still not a businessman, and was happy to hand off the trouble of developing Computer.com and the 1-800-COMPUTE phone number that was part of the deal. He'd rather work with the two electronic mailing lists he developed for sick children.

"To me, money's a way to continue the lifestyle I already have," Sinclair says. Despite the half-million windfall, "if you come back here in two or three years, we'll still be here, in this little two-bedroom house."

Unless, that is, Computer.com goes public, and his share is worth serious money. Then, he says, "we'll get a bigger house, and a Porsche. Isn't that just human nature?"

CAPTION: Kevin Sinclair paid $40 to register the Web address computer.com five years ago. A couple of weeks ago, he sold it for $500,000.