I for one can't see how the OS, in this case, Vista will make games run any faster. It's hardware that does this work for us. For example; the game Oblivion. It's both CPU and GPU dependent. The faster your CPU and video card the better the game plays. The OS is the platform for letting you run the game, but it's also using up CPU and GPU cycles as well.
If you press the Ctrl Alt Delete key at the same time you will get the Task Manager to come up. Now you can see things like, Processes, CPU Usage and the Commit Charge.
Commit Charge lets you know how much RAM is getting eaten up.
On my rig, I have the following-
Processes - 43
CPU Usage – (This always Varies)
Commit Charge 320M / 2460M

If I shut down several things that I don’t need running, I can get to a
Commit Charge 265M / 2460M

Then when I’m running Oblivion my Commit Charge is, 661M / 2460M

I’m guessing if I closed down my anti-virus and third-party firewall I could save a bit more, but that still means the OS (Windows XP) is using a Commit Charge of 250M.
Now Vista is even bigger and flasher, and even if you can turn some ‘stuff’ off or down, it’s got to be using more CPU and GPU cycles.

Everything I’ve read says my rig will run Vista, but I’m not convinced that it will let me run Oblivion at the frame rates I’m getting now. Now if I have to start turning things off or down in my games that would be unacceptable. The OS is there to assist me, not hinder me.
And in the new issue of PC Magazine (Dated May 9), they have a “Truth behind the Delay of Windows Vista.) and in there they say one of the reasons is ‘concerns about performance.’

I’m going to take a ‘wait and see’ approach.