Actually, on a 2 core / 4 thread cpu while those threads are supposed to have their priority reduced, in my testbed watching performance counters indicated that Vista was indexing, defragging, and doing all kinds of other background tasks without properly throttling. I've actually watched Enemy Territory's thread go from normal to low priority hundreds of times a minute as Vista can't make up it's mind what it wants to do. These tests didn't suffer as much on a single core, single thread platform.
Did you try running the tests with those background tasks disabled? If so, did gaming performance increase? If it did, I guess I have to eat my words. I had assumed Vista would have all that sorted out, hopefully future updates will solve that.