All of nVidia's earlier products have trouble with the latest (Shader Modelling Two) games, and the low end of the sixth generation continued that trend (6200, plain 6600). PCI as a "video bus" is extremely slow, so although the X1300 Pro cards for either AGP or PCI-e aren't totally useless for some low-demand games, those capabilities are effectively cut in half, or worse, for plain PCI. Both ATI and nVidia have produced IGPs that are better for games than actual cards, when those cards are crippled by PCI's slow speed.
Do avoid the FXes. nVidia literally BROKE that design's SM 2 capability when they rejected the official Microsoft Dx9 specifications for shaders.