Ati drivers don't have an 'off' setting, you can turn off adaptive AA and AF but the best you can do to disable them is set them to 'application managed'.
__________________
Core 2 Duo E4300 @ 2997mhz (333x9 @1.3250v) (66.5% Overclock, stock voltage), Arctic Cooling Freezer 7 Pro, 2gb PC6400 OCZ Special Ops (5-5-5-12 @ 2.1v) @ (4-4-4-10 @ 2.0v) @ 667mhz, Gigabyte GA-965P-DS3 rev 2.0 F13 BIOS, Coolermaster iGreen 430w PSU, Sapphire X1600 pro 256mb DDR2, Samsung SpinPoint 2504C SATA 2, Samsung SH-S183A DVDRW, Vista Ultimate x64 SP1