@ Paul Delaney
Expecting it to actually run on that spec is probably a bit optimistic though! Remember that at the time the P3 was released, we were all using Windows 98 (shudders at the thought of those days); there's been a fair few Windows releases since then...*
I agree the minimum (MS quoted) spec is not good enough as always, but from my tests on quite a variety of machines it will definitely run happily on a lower spec than Vista. I probably won't chuck it on anything earlier than a P4, but I don't really have any front line machines older/slower than that anyway.
It will take a lot to tear me away from XP as it's rock solid when I set it up as I like it, but it is getting old and unable to use the latest hardware to its full capabilities, so I'm going to have to upgrade sometime. Vista was too much of a resource hog for me but I think I will be purchasing quite a few copies of 7 quite soon after it comes out (and it's rare for me to be an early adopter). My main reservation is still the abject lack of classic view for those of us who view our computers as a tool rather than a pretty multimedia experience that wants to make friends with us!
*I believe it's somewhat frowned upon to mention the name of Windows 98's successor in polite conversation, so I've omitted it to save everyone having horrible flashbacks and panic attacks.