Im not sure whether it is connected someone from here will no doubt come back on it. But my understadning is that AVG would not be equipped to erase the Nachi worm as I know there is specialist tools from symantec etc
This is a problem that I found existed under Win98 unless using the very latest version of IE fully patched. It does seem to hold some truth under XP as well, though not sure of the fix. If you scroll hard and fast enough you can get your free resources down to nowt in Win98!!
Make sure IE is up to date and there are no other updates recommended would be the first step. Then I guess looking at the graphics setting and perhaps some of XP's other "tellytubby" features and see if they can be increased/turned off to help.