avast v8.x minimum OS requirement is still Win2000 (yes, some features won't work on Win2000 or WinXP SP0/SP1: e.g. autosandbox, sandbox, safezone; you'll have slower file-system shield, etc). Official note about XP SP3 is not correct (there're still some win2k users on this forum). As for avast 9.x, users with Win2000 won't be able to install this version -- we'll use a newer development kits which can't produce a code which can be executed on Win2000, but XP SP2 should be still supported. Our statistics are as follow: we have 33% XP users (22% with SP2, 78% with SP3).