He certainly doesn't need all that to play WoW... hell, my $400 Dell can run WoW without lag.
I would recommend just upgrading your video card. I'm currently running a 7600GT and it will run WoW fine without lag. It runs BF2 fine, and that game requires a lot more juice.
I know. It wasn't that expensive, though. The tower with the majority of the required parts was something like $1,100, which I think is pretty reasonable.
I wasn't recommending he go balls out on every component; I think it's wise to purchase things that are "better than average" (but not ridiculously awesome) if you plan to use it for a long time, though.
To be more precise, I was running Bioshock with the graphics cranked with absolutely no latency, and this was with BOINC running at full blast in the background.