Viruses generally do not attack graphic memory as far as I am aware...
WC3 will run perfectly on 64 MB of graphic memory, unless...
1. You are running at some insane resolution (like 1080p HD).
2. You are running vista / 7 in aero mode.
3. Your graphic drivers are a piece of shit, which intel's generally are, atleast with that age of card.
Just stop for 1 second and pick up the box.... Does it say "recommended, 512 MB graphic card" or something stupid?
It says, minimum - 8 MB graphic card (READ THAT, 8 MB ONLY) followed by some voodo and a TNT graphic card (both these brands no longer exist).
For mac, it advises 16 MB (not 128 MB).
For recommended play it advises 32 MB (not 64, 128, 256 or 512 MB, just 32 MB).
Thus, unless he is running other features to consume graphic memory like funky desktops that vista and 7 use or running at a totally insane resolution, there is no way his graphic card does not have enough memory.