You can try the beta drivers, I think it's 10.7a.
SC2 made my settings to Ultra to default. Too bad I can't play it since I didn't buy a copy. However, my friend and brother played since they both do have copies. Now my friend wants me to help build a computer for him so he can run on high instead of low.
Desktop -Cooler Master NV690/AMD Phenom II X4 965 BE/MSI 880G-E45 Motherboard/2 x 2GB DDR3 G.Skill Ripjaws X/Sapphire HD 5870 1GB GDDR5/CORSAIR CMPSU-550VX/Seagate 7200.12 500GB (OS), Samsung F3 1TB (Storage)/Sony DVD Burner/Windows 7 Professional 64-bit