I would not advise using the 64-bit version of Windows at this time. The performance is not noticeably better and the lack of drivers is more than a little annoying. I accidentally installed a version of it on a homebrew computer I'd made a few months back - didn't notice the disk I grabbed was 64-bit, and after I discovered the mistake decided to experiment a bit.Has anyone had experience with running AutoCAD Lt 2006, enercalc, Ram and other engineering programs on a Windows XP Pro 64 bit edition. I am thinking of upgrading my computer, and am not going to go to Vista but would at least like to get to the 64 bit systems.
Unless you have very "regular" equipment, you run quickly into a big problem. For instance, I have an M-Audio card that can be used for "pro-sumer" level audio recording, and there are NO drivers for 64-bit Windows AT ALL, re the M-Audio website. Lots and lots of other "niggly" annoyances along the same vein.
Get your 64-bit system, and make sure you stock it with 4 GB of RAM. You'll be fine with 32-bit Windows, even though it "only" can address that 4 GB. But it's hardly the same thing as when we reached the 1 MB limit of 16-bit processors back in the day.
(N.B. as for Vista, based on my brief experience installing IT on my experimental machine, I wouldn't wish it on my worst enemy!)