I would download Driver Sweeper, uninstall your current drivers, boot into safe mode and run Driver Sweeper (just read the how to use on this page).http://www.guru3d.com/category/driversweeper/
I would give that a try and then install the latest or whatever drivers you want. I am currently still hanging out on 10.4 because the others give me weird issues in Bad Company 2. Stupid ATI drivers. I've heard many people not going past 10.5 for those reasons.