Computer books are a big business. Thousands are published every year, explaining how computers work and teaching the ins and outs of particular programs. I'm guilty of writing a few myself.

The latest wrinkle in computer books is the book-disk package. That is, each book has a disk glued into a pouch inside the back cover. Oh, it's been done before, for years, really. A book about programming would be chock full of program examples, and you could choose to type them all into your computer -- a Herculean task and a superb opportunity for typos -- or to buy the copy of the book that came with the examples already on a disk. Often the book alone would cost $20 to $25 and the book-disk package would cost $45 to $50.

Last month, a pile of new books from Microsoft Press, many of them with disks, showed up at my house. Microsoft Press is a division of Microsoft Corp., famous for the DOS operating system, Windows and applications such as Word and Excel.

Many of these book-disk bundles, however, don't follow in their ancestors' expensive footsteps. They cost only a little more than the average computer book does without a disk and offer a lot more.

Some of these books are "template" collections, with the templates collected on the disk and explained within the pages of the book. Templates are essentially programs. They are computer code that customizes a general-purpose program.

The "Money Manager" books from Microsoft, for instance, offer spreadsheet templates that can animate a standard spreadsheet program to help you calculate and analyze your financial dealings. You need a computer that will run the appropriate spreadsheet program, then you just load the template and follow its directions. By combining one of these template collections with your spreadsheet, you have many of the functions of a dedicated financial program such as Managing Your Money.

One advantage of the templates approach is you get to use the spreadsheet skills you've already built up instead of learning a new program. You also get to easily and immediately move your financial results to spreadsheets you concoct yourself. And you can customize the template.

One disadvantage of the templates approach is that few templates are as neatly organized or as smooth in action as a dedicated program. And templates are useless if you don't have the host spreadsheet program.

I tried both Lotus 1-2-3 Money Manager on my PC and Microsoft Excel Money Manager on my Mac. Both are by the same author -- Stephen Nelson -- and cover the same territory -- taxes, investments, loans, savings, insurance and the like.

The books are generally easy to follow, and the templates are easy to load and run. Some templates are little more than short spreadsheets with a few equations to figure interest rates and the like. Some templates are more elaborate, with macros that run themselves, nearly converting the spreadsheet into a dedicated program. The Mac Excel template package includes graphics such as charts that you won't find in the PC 1-2-3 package.

I see two reasons to buy one of these template collections over buying a dedicated financial management program. First, they're cheap -- if you already have the spreadsheet, that is. For $34.95, you'll get 75 percent of the stuff in a $200 financial management program. Second, they can teach you more about your spreadsheet. You can open up the templates and macros and study their guts. The book explains how the sections work and how to customize them.

But if you're not interested in poking into the innards of a program, and you want a slick package that doesn't demand extra time and attention or spreadsheet smarts, you should bypass templates and get a dedicated program.

Then there's the other kind of disk-book package from Microsoft Press: the tutorial books, guides to learning and usingparticular application programs, such as Word, Word for Windows, Excel and Works. What makes these books different from the competition is they come with a "working model" of the application program. These books cost $29.95, at most $5 to $10 more than competing books. And for those few extra bucks, you get a copy of a program that costs $200 to $500 on its own.

What's the catch? Well, the programs aren't complete.

For instance, the book version of Excel for the PC will only work on a very small spreadsheet area. The book version of Word For Windows is missing a bunch of features, such as the spelling checker, and can't handle documents longer than two pages. And you can't get any technical support from the company with these working models.

I tested the Word For Windows book. It was easy to set up and run. And remember, this means you're getting a test version of Windows, too. Word For Windows calls for an AT or better with at least 640 kilobytes of random-access memory, a hard disk, DOS 3.0 or later, and an EGA or VGA graphics adapter.

The book, written by Michael Boom, is good but not great. As all these books do, it starts with simple features, then steps up to the more advanced stuff. You learn to start the program, enter text, edit text and to format and print the results. You can do this with a full-blown copy of Word For Windows at hand, or you can follow most of the text just using the model version of the program.

Who should buy this book-disk package instead of some other Word For Windows book? I'm not sure. Essentially, it's a tutorial book with a demo version of the program. In most cases, if you care to learn Word For Windows, you presumably already have a regular copy of the program on your computer. If you just want a demo, then why buy an entire book with attached disk? Especially when some of the vital advanced features are crippled?

My take is that Microsoft is using its cozy relationship between the company's program side and the book publishing side to try to get an edge in the book market, and it shouldn't. This book-disk package is too expensive to be a demo and a waste of disk if you already have the program. Shouldn't it be a waste of book if you have the program, too? After all, if you have the program, you have the tutorial and reference manuals that came with it.

If you need a tutorial book, compare the ones available at a bookstore to see which fits your style best. If you want a demo, go to a computer store or show and play with the program for a while. This book-disk package deal isn't such a great deal for most people -- it's more a marketing ploy.

Phillip Robinson is an author of books and articles about computers and an editor for Virtual Information of Sausalito, Calif.