Most PCs that are less than 3 years old should be able to run it without problems, though less than 512MB memory will be noticeably slower - suggest at least that.
PCs with less able graphics WILL be able to run Vista, they'll just have to turn off most of the eye candy (so games written for Vista won't run).
WARNING: Vista looks like an interesting OS to me - MS have finally got around to fixing many of the previous security and many other issues, but there's a price (of course!). XP/2000 drivers won't work in Vista - so you'll need new drivers for all your devices. If your vendor isn't going to develop one then you're outta luck - and only MS certified drivers will be allowed, with NO option to allow installation of unsigned drivers (MS charges for certification and it takes quite a while).
DRM: Vista will have pretty aggressive Digital Rights Management, not just for music and video, but documents and images as well. If you don't mind not being able to do a lot of the things you once took for granted then be my guest.
Privacy: If you ever bothered to read the MS EULA (End User Licence Agreement) that comes with your MS OS/software you know that you effectively sign away pretty much ALL your rights by accepting it. The OS can watch what you are doing, phone home and use the info as MS sees fit - misbehave in MS eyes and your OS will be disabled - your habits WILL be know to MS.
I wouldn't be caught dead near Vista, not because it isn't a clever and pretty OS (and the indications are that it will be) but because I don't like MS's attitude and business methods, I think that they are far too powerful for their own good and ours, I don't trust them one bit and I don't like DRM and the feeling of the loss of my autonomy and privacy. And Vista will be expensive. But hey, whatever floats your boat....
MS are terrified of Linux and are using every means at their disposal to hinder the steady adoption of Linux - fair (a bit) and foul (a lot) - bribery, lies, innuendo, payoffs, threats to vendors, perversion of web and document standards and lawyers, lawyers, lawyers. Nasty.
Example: developers who plan Linux and MS versions will find that their MS certification will take a l-o-o-o-o-g time - probably enough to ruin them. If they promise not to develop for Linux they'll get a big discount on the certification fees. Don't laugh - it's happening right now, and MS has been employing these bully-boy tactics for years.
Example: MS is just ignoring the AntiTrust judgement against them in the States - they've bought off the supervisors of the judgement and with Vista will just sidestep the whole thing anyway.
Example: MS were ordered by the EU to release the full documentation of the XP program interfaces so that non-MS software writers could compete with MS. What MS then did was to offer to licence (for hefty fees) part of the source code (not the same as documentation and pretty much useless for writing apps.) for XP (which Vista will render obsolete anyway). And the huge fines? MS can afford it, even though they would bankrupt a medium sized country.
MS's army of lawyers and their bottomless pockets mean that legally only perhaps IBM could take them on in Court - with any other company or individual they just drag it on until your money runs out and you're bust.
GNU/Linux is roaring ahead with improvements in usability and user-friendliness, is rock-stable, already secure, unencumbered by DRM and I'm in control and can tinker as much as I like. No fees, no EULA, no phoning-home with my info. If I need to run Windows apps., WINE (the Windows Emulator) is getting better daily and can now run the majority of Windows programs (many of which are now cross-platform or are being ported to Linux anyway now). Linux apps are mostly GPL (so free) and those that aren't are at a fair price and compete fairly.
Finally, the Mac OS is now out for the x86 platform and it'll only be a matter of time before Apple releases it for non-Apple PCs (it'll be expensive though).
So no, I won't be going to Vista.