Antivirus slows boot

[Choy]

I'm experiencing very slow boot ups. Getting to the logon screen isn't usually bad, but after logging in and actually getting a responsive system. Upon checking I've noticed that it is the antivirus (AVG Free) that reads 6 gigs of data from my discs immediately after logging in. That makes the computer very slow for the first minutes. I've tried other antivirus software with no change. Is there any way around it? Or at least reduce the load so I can use the computer earlier. Or is there another reason for my problems?