Sorry, but AVG is pretty much useless against the most common viruses these days. Many programs are.
I would recommend the following trio of programs for virus / malware protection / removal under XP:
* Microsoft Security Essentials. Its a free download from Microsoft, it does real-time protection, and it will catch most older viruses. Won't catch the new ones, but neither will AVG, Norton, or McAfee either.
* Malwarebyte. Catches most newer malware. Free version doesn't do real-time, so run it every few weeks or if you are suspicious. Remember to update it before running it. A free download from Download.com:
Malwarebytes Anti-Malware - Free software downloads and software reviews - CNET Downloads
* Combofix. The best "nuclear" bomb to drop on tough virus problems. Doesn't work (yet) with Windows 7. Only download it when you are ready to run it, because it changes every few days, you can find it here:
Bleeping Computer Downloads: ComboFix Download