Well, we'd really have to know more about his computer before recommending him to buy a new rig

It's quite possible that he'd do quite well with a ATi 9800Pro or the equivalent Nvidia product. Screw it, I'll make a link:
Link
Above link compares various 3D cards.
Price comparisons (on ebay, common "buy now" prices):
ATI RADEON 9800Pro 128MB = Good card, too old to buy, really
ATI RADEON 9800XT 256MB = $150 (I know this card runs this game well)
NVIDIA 6800GT (AGP) = $190 (better than the 9800XT)
NOTE: On older/cheaper motherboards where you can't fiddle with the amount of juice that goes to your AGP card, you're system will run more stable if you set it to run at 4X instead of 8X. You'll only lose about 3 FPS (seriously), and might make the difference between a stable and unstable system. YMMV