I have a ati mobilty radeon 9600, and have had little trouble with it, so I'd suggest giving it a another try before getting a new card...
there will be heaps of topics on this allready, but this looks like a good start:
Edit. if you have tried this before, or have any problems can you post the ouput of
cat /var/log/Xorg.0.log | grep EE
cat /var/log/Xorg.0.log | grep WW
....also, you may want to post (some of) you /etc/X11/xorg.conf file