I hope it's cheap ( $400?), and PCI express rather than old discounted model with AGP. (to upgrade the card later)
if he gets it, tell him to buy a second 512MB stick at the same time.
geforce 6600 is quite decent, not bad to play doom3 or far cry and infinitely better than the X300SE or 6200TC you usually see on these branded PCs.
For latest, stupidly power hungry games such as oblivion, graw, fear it's gonna be a bit limited/painful (but should run)
pentium 4 3.0ghz is decent (and runs hot) but every other CPU is better for gaming now.
so, if it's cheap, silent, nice looking and he can change the graphics card later, why not.
a custom built PC would be better.