The problem I have with the low range NVidia cards in the 5000 family is they advertise the same features as the bigger brothers (5950 and such). So a game will use those features, but slow down horribly due to it. A friend of mine bought a 5200 for a system to run Everquest, and it ran worse since Everquest tried to use newer direct x 9 features on the board. He replaced it with a Radeon 9200 and saw a preformance jump, because the 9200 didn't support those features.

That was why I said 5600 and above on the NVidia side. The ATI cards like the 9000-9200 will run Doom 3, but still pretty poorly. 9500 and above on ATIs side start having the features and power Doom 3 craves.