When she received the e-mail order from the Sultan of Brunei for a party of 160 celebrating his son's birthday, Jan Jewell had a good idea just how far the Internet had taken her party-planning and party-supplies business.

There are more reliable measures: As the leading online provider of birthday party goods and services, BirthdayExpress.com boasts more than a half-million customers and ships more than 1,200 party packages daily. More than 3 million people will have attended its parties in 1999. Seven million of its catalogues are sent to homes with young children annually. A readership poll conducted by Child magazine rated it second only to Chuck E. Cheese as a birthday-party resource.

"It's really an incredible challenge to make birthday parties happen, to do something fun, and to think of different things to play each year," says Jewell, a mother of four whose frustration with pulling together her own children's parties inspired the birthday-assist business.

At BirthdayExpress.com's Web site, customers can choose from 111 party themes, ranging from currently popular Madeline, Pokemon and Blue's Clues to activity-based baseball, bowling and art parties. For instance, order the $56.30 Scooby-Doo Deluxe Pak and get eight settings of Scooby-Doo paper plates, cups, napkins, table cover, balloons, and color-coordinated utensils, decorative curling ribbons and crepe paper streamers, a Scooby and Shaggy cake topper and candles, a 10-inch plush Scooby that doubles as a centerpiece, and party-favor bags.

While BirthdayExpress.com trades big-time in licensed tie-in items, about 40 percent of its products are its own exclusively, and many are manufactured by the company. Its distribution center in Kirkland, Wash., typically assembles and mails orders within 24 hours after receiving them. Included in each package is BirthdayExpress.com's party-planning guide containing more decorating ideas, activity suggestions, and theme-related recipes for snacks.

The site also offers seemingly endless thematic accessories, including invitations, thank-you notes, party hats, games, T-shirts, sticker albums, costumes, pinatas, craft kits, toys and gifts. And for organizing needs, its "Party Tips" section provides an electronic checklist to track all the to-dos starting four weeks prior.

"We can have just an infinite amount of information online, it's available to anybody and it's free--you don't have to buy anything," says Jewell, who with husband Mike Jewell established Birthday Express as a direct-mail catalogue business in 1994 to pave the way for its online incarnation about a year later--when conventional wisdom still maintained nobody could make money on the Internet.

But if no one online holds a candle to BirthdayExpress.com, it is no longer the only party in cyberspace. In fact, the online party-planning industry is coming of age. "Last December, less than a year ago, one in every 60 of our orders was coming in over the Internet," says Jewell. "Today, it's one in every three."

Those eye-opening numbers are attracting newcomers who are bringing their own bells and whistles to the virtual party world. In early October, for instance, start-up party and celebration sites iParty.com and GreatEntertaining.com joined the crowd. And in July, a Gaithersburg-based firm launched ThePlunge.com as a virtual hub of party announcements, planning and invitations. Predicting it will be the most comprehensive online party site, eParties.com recently announced it will launch its "party portal" before the end of the year.

Catering more to adult partying, Party411.com has been promoting "Millennium Mayhem" bashes this month. And Partysmart.com, the virtual shopping annex for 150 brick-and-mortar Paper Warehouse and Party Universe stores, provides online access to party-planning experts, online tools such as Date Reminder and Invitation Maker, and ready-to-order, thematic party packs.

"It is a validation of how robust the market is to see the number of entrants getting into the market," says Sal Perisano, CEO of iParty.com which, he says, has raised $23 million to fund its business plan. Perisano plans to direct $10 million into national marketing online and off-line to establish it as one of the top players.

"This is a $10 billion industry without a recognized national brand," explains Perisano, who in 1992 co-founded with his wife, Dorice Dionne, The Big Party--a 51-store party-retail chain in the northeast. Now the couple is building iParty.com to handle everything from bar mitzvahs to tailgate parties. "In the greeting cards sector, there's Hallmark; in the toy sector, there's eToy and Toysrus.com. In our sector, there's no one national brandname. We intend to be the dominant one within two years. Quite frankly, we feel were in a good position to do that."

His target? "People who want to throw a party," says Perisano, who has a personal affinity for the Groucho glasses he sells among iParty.com's growing inventory of products. "Whether it's a Winnie the Pooh party or Star Wars party, an adult party, or just that you need an extra pair of Austin Powers teeth, we live this stuff."

Creating a new and different online party business is no piece of cake. But if originality counts, Bethesda Net entrepreneurs Guy Wolcott and Keylan Qazzaz take the cake with their party-evolving ThePlunge.com. "We're getting about 2,000 people a day coming to the site, both browsers and customers. We've had about 3,000 different events so far and we're really just getting our marketing started," says Wolcott.

What The Plunge.com currently offers customers is their own personal party-related Web sites, where they can announce it, invite guests, carry on chats, give directions, even follow up with memories and photographs. Package deals range from a basic "two-page" site for smaller events that Web designers Wolcott and Qazzaz will create for free, to full-blown wedding sites that cost $45.

Meanwhile Jan Jewell says, fine, let the party begin. Last month, BirthdayExpress.com announced a $25.1-million national expansion, with $13.1 million coming from venture-capital firms. On Tuesday, it launched CelebrateExpress.com, a new site that offers party products and supplies for adult birthdays, holidays and other special occasions.

Says Jewell: "As far as these other party businesses are concerned, they are pretending that we don't exist. And that's fine with me."