Video card matters the most by far. The thing is, the video card is the most expensive part too, so if you don't spend a lot on a video card, but have 2GB of RAM and an FX-57 CPU, your gaming performance will still suck.
You could have a $400+ video card yet your processor and RAM be average, you will still get very decent performance, althought not AS good as it would be with the more expensive CPU/RAM.
Look at it as if the RAM and CPU provide re-inforcements for the video card.