My XP CD is service pack 1, meaning no firewall, old old version of XP, and old version on internet explorer.
I'll get malware within 5 minutes on it. Did you install AVG from a disk or did you go online with IE to get it? Makes a big difference.
So when I reformat, first thing I do is have service pack 2 installed from a cd, then temporarily use zone alarm firewall to be safe, then install avg, spyware blaster, spybot, and a squared, and firefox. Once all those are set up I make sure automatic updates are on.
I don't surf the web just wait for the yellow icon to turn on & install windows updates automatically.
Reboot finalize windows updates, defrag & then your set up, so for me to reformat is a pretty big pain.