I have a 9800 XT pro and got it to work yesterday using the ati drivers right from their site. I followed the following advice I got from a Ubuntu forum (http://ubuntuforums.org/showthread.php?p=5748110
"Good news for the people suffering this problem. In a last attempt, I found the - very simple - solution.
1. Ati released a new driver for the card which can be downloaded from their site.
2. sudo sh file-of-the-driver.run
3. Reboot - maybe this is not necessary
4. sudo aticonfig --initial
5. Reboot and enable compiz-fusion "
Just FYI, I did not reboot in step 3. Not sure if this will help you, but figured I'd post my solution.