Shit, I used to play a bit of WoW not too long after it came out. Performance was more or less on par with Windows -- FPS higher on Linux in some places, lower in other. Best thing was that with multiple desktops I was able to tab in and out in milliseconds, something that always seems to take ages on Windows.
Then again, I did it on Gentoo installed from stage1. Took me a few days to compile everything, and cost an hour when there was a WINE update, but it ran well.
If the submitter is still around, I'd second the advice given in other places. Give your kid the install disc, and let him handle it. Sure, he'll probably have to start from scratch a few times, but installing Windows has never been easier. If your kid has a few geeky friends that run Windows, even better -- they should be able to explain what are common signs of malware.
If he's used to Linux, he might be able to figure out how to run WoW with WINE when he tires of Windows.
I rarely use Windows (although more often than you seem to), and I'm starting to feel outdated, but I tend to go with Microsoft Security Essentials and Avast (they have a free edition). If not Avast, I've heard good things about ClamAV on Windows.
If I recall correctly, a WoW install has no real ties outside of the program folder, so it might be a good idea to make a backup of that folder once in a while. If the system goes down, just copy it and you're set.
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