Sean’s note: Confusing, isn’t it? If you already have an installer disc for your current version of Windows, you can easily get away with the upgrade version of Windows Vista, even if you’re planning to install Vista from scratch… but you’ll have to follow some odd procedures (since Microsoft no longer allows upgrades without a previous version installed). Paul Thurrott documents this process on the Super Site for Windows. http://www.winsupersite.com/showcase/winvista_upgrade_clean.asp - note that this technique allows you to use the Vista upgrade even if you don’t have an earlier version of Windows. So you should probably buy the upgrade version.

You probably don’t need the 64-bit version unless you’re running 64-bit hardware and you’re willing to deal with quirky performance occasionally. The vast majority of users will get along perfectly fine with the 32-bit version. You’ll want to ask that the OEM version is upgradable down the road…it should be, but double-check…otherwise what you’ll get with the OEM package is more streamlined packaging and less documentation….the only catch is that you may have to buy another piece of hardware at the same time to make the transaction legitimate.