Just saw over at MaxReboot that the latest Windows XP driver for ATi Radeon has been leaked. This is the 6.13.10.6018 driver dated January 8, 2002 that ATi developers has been playing with for a week or so now.
According to the users who already tried this driver, you can now adjust anisotrpoic filtering within the driver control panel (2X to 16X). Performance is said to be close to that of the 6011 driver. Learn more about the users comment on this latest leaked driver over @ Rage3D