Try turning off compressed textures and triple buffer. Also, if you have Anti Aliasing (whatever ATI calls it now) turn it to off in your video card settings. I'm running a TI 4600 and it's smooth as silk.

What exactly do you mean by Anti Aliasing? Do you know what ATI calls it now?

I'm having the same problem as mentioned. I also noticed it in some MP maps, that could bugger up MP play. I'll muck about in my settings and see if I can improve things, hopefully that'll help.