It isn't about your video card, Unreal in D3D is all CPU. My system isn't great in Dues Ex, and it is really fast. Turn off detail textures in graphics, and it will make it playable. 32bit does make a big difference in that game, a lot more than in UT.
I beat it yesterday, it was a great game, it took me about 18 hours. Only the 4th shooter I've bothered to play to the end (Doom 2, Goldeneye, and Half-Life are the others).