Running games under Wine generally cuts performance in half because the drivers are lacking lots of optimizations. If he's barely able to run it on Windows it'd be a slideshow in Linux.
I second this. Wine has a fuckload of overhead. I have a computer with a 2.7GHz Athlon X2 with an overclocked 8600GT (512MB) and I need to set most settings to half of what I can use on Windows. And due to regressions in wine I had to run it in DX8.1 mode (I do it on Windows too though for better performance) to even get the HUD to show up. Sure it's tied to a specific version of wine but still, the general rule is that gaming under wine sucks and simply isn't enough to convert a gamer to Linux.