You might be talking about CUDA
. CUDA is only supported by nVidia cards, and if you have a 8xxx series or higher, your card should support it. Full list here: http://en.wikipedia.org/wiki/CUDA#Supported_GPUs
However, the application you're using must have CUDA support to take advantage of this. There are H.264 CUDA encoders out there, and I believe Premiere CS4 has support for it, but if I'm not mistaken the quality probably won't match what x264 can put out. And AFAIK x264 doesn't support CUDA.
My advice would just to stick to x264 and get the best multi-core CPU you can buy (Core i7 comes to mind).