IDK if this is still the case with RTM. I used to run Vista beta on a slower laptop with less memory and it was easy to note differences. What I noted during the *beta* on the slower computer was that turning off things I wouldn't want to turn off like system
restore, windows defender, uac, defrag, indexing all together gave notable perf boost. However on 4 GB c2d at 2.4 ghz or more the overhead of above on RTM is not enough to warrant losing any one of those.
Nevertheless XP feels still clearly faster than Vista on that old hardware even with all the useful services turned off (I ran the lappy with RTM for while before going back to XP). This could be explained by Vista being compiled with newer compiler that produce
slower code for older computer and faster for Core 2. More likely explanation is that there's still a ton of new lower level stuff in Vista that has very little overhead but with slow system gets more pronounced. I've noticed that 1.6 ghz core 2 is clearly
horribly slow compared to 3 ghz core 2. Really need that 2.4 min to make Vista usable though I think to get snappy Vista you need 4 ghz or new i7/Nehalem. And those new Intel SSD of course.
2008 just seems more responsive to me, probably because it comes with a lot less stuff turned on by default. Less is more. Like Raymond Chen says, "Doing nothing is really fast!"