most important is cpu and ram. and as long as you dont use 10 hiRes models with each 1-2k diffuse+normalMaps on them and need to see it realtime in your modeling panel using highQuality settings - graphic card really doesnt matter from my point of view. it is good to have quite a bit of RAM on your graCa but in the end it depends on your needs. some time ago I got a new QuadroFX 4500 at my office, and guess what.. the only difference I noticed was that I could then plug in 2 monitors instead of 1 with the old card. there were no other performance improvements.
if you start - buy a midClass gaming card anbd spent your money on a quadCore or high dualCore CPU + lots of RAM. the more the better.
gl!
everything starts and ends in the right place at the right time.