Sassy,
Steps to take:
1. Find out if your computer has a parallel port. If so, you can use both a printer with a parallel connection and a printer with a USB connection. Some modern PC's don't have a parallel port anymore, and quite a lot of printers only have USB.
2. Think about what kind of printer you would like: inkjet or laser black and white or laser with colors. Photo's only? Or primarily non-photo's?
3. Assuming that Vista is out for more than half a year now, practically all new printers you can buy should have Vista drivers. So if you've selected one (big names are Canon, HP, Lexmark, Epson, but there are others) all you've got to do is ask in the shop if they are sure it has a Vista driver. All they've got to do answer it is look what the box says about it, so that isn't too difficult a question.
If you decide to buy it in an Internet shop, the product specification should mention it. To doublecheck, you can have a look at the manufacturers site (like www.canon.com) if they offer a download for a Vista driver on there support pages. If you buy PC and printer at the same time (say, at Dell) they're sure to work together, of course.
Hope this helps.
Kees