I've got a report from 2 users that avast! causes massive problems on vanilla WinXP systems and systems with just SP1. From their words, installation was started but system either restarts during installation or installs but then causes massive problems on every boot.
I don't have any SP0 and SP1 XP systems at hand to test, but it would be good to verify that installer actually checks for this and prevents installation in cases where minimal system requirements aren't meet fully, to avoid raging of users.
Please verify this. I know there aren't many such users but still, avast! still supports WinXP and as such it has to work correctly and notify users of it can't.