Just saw over at MaxReboot that the latest Windows XP driver for ATi Radeon has been leaked. This is the 18.104.22.16818 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
Download: ATi Radeon Winxp driver v22.214.171.12418
Download: Also a link @ Warp2search for the driver
News source: MaxReboot