I had this problem too. I turned on AA in ATI Control Center but AA is disabeling after Alt+Tab (or Ctrl+F4) movements. I know, this is not LFS problem, in W2k it worked fine, but now AA working bad. Maybe it is problem of WinXP, maybe new drivers have something - i don't know, but there is somethig strange
P.S. My G.Card is Saphire Radeon 9600 (256 Mb)