Many inmates run their setups like this and it is possible to have a PC run up to 9 monitors (although I'm sure developments will increase this number). (16, under W2K and XP at last. --Tyberius Prime
What you need to do is look for dual-head video graphics cards. Most of the big manufacturers (Nvidia, ATI, etc. make them and Matrox now offer cards which will work with 3 monitors(4 monitors - but horribly expensive). Have a look around for reviews and compare prices to see what suits you and your budget.
It is also possible to add a second graphic card and plugging the second monitor into that card.
Old S3 Graphics cards which you can pick up dirt cheap on ebay work, although they must be the graphic's adapter your PC boots from, which usually doesn't mess things up, since you can change the 'primary adapter' in Windows 2000/XP at any time.
Older Matrox PCI Cards work like a charme as well.
As of the time of writing this FAQ was number 1 at Google for a search using the terms how, to, run, two, monitors (and variations on that) and 6 for the terms two monitors.
