Well on the bright side you've got a slightly better card than you thought then
Anyway, yes it's very odd that it should behave like this.
I'd try reinstalling CS (as this is clearly a CS issue, if other games are working) in case it's somehow got tied in to the old card. Also, try the 3 different rendering modes and tell us what happens.
Software should look crap but run quite well, and OpenGL and DirectX should be about equivilant to each other. Don't use the minigl driver if the option is given, as that is for old 3DFX (voodoo series) cards.