Yes, ATI generally works better with Intel CPUs and Nvidia works better with AMD processors. I don't know how much of an effect this has on graphics cards' performance though. I wish I would have known this, I would have surely gone with Nvidia.
sigh, you can use either nvidia or ati cards with either intel or amd procs. i use an nvidia 6800 with a P4 3.2 and couldn't be happier. i don't know where people get this notion that one is better than the other if paired with a certain chip.
The chips themselves are fine, but ATI often gears their cards towards the features of the P4, while NVIDIA often works with the features of the AMD chip. The cards will accept either processor, that's true.