I guess my misconception comes from my previous experience with AVG 6.0, which always showed a scan screen during the bootup and would declare no virus found before continuing the boot process.
Well, if I'm not wrong, AVG works at
logon time of Windows 9x\Me.
Even when there is only one user, it happens
after the operational system (drivers, etc.) were loaded.
We're talking about
boot time, which is only possible in NT systems. SpyBot, for intance, works at
logon time of XP