Quake 4 a computer game?

I have a compaq with ati radeon xpress graphics which don't work with Quake 4 and I need a new graphics card any ides I'm thinking around something for $60 or 70. I can kinda see a picture but when i move while playing the game it's black dotted and moves slow and I know it's not the cd because it has no scratches and no problem reading it. So help me and I'll see who has the best answer in 4 hours.