I will disagree with the "too fast for your machine" statement regarding the 7800 card. Even when cpu limited, a faster vid card will let you turn on antialiasing because that takes almost no cpu work but dramatically improves graphics quality.
Even with an AMD 3700 and an nvidia 6800 GT, my computer is "cpu limited" in AH. Dropping screen resolution gives me ZERO framerate increase. By your logic, that means my video card is "too fast" for my cpu! Utter garbage. Instead of wishing I'd bought a cheaper vid card, I just enabled FSAA. On my computer, the sweet spot is 2xQ FSAA although I can live with 4X FSAA if I turn down the sliders a bit. In any case, running AH with FSAA enabled is a much better gaming experience than running without FSAA, and that's why I strongly say that there is no such thing as too fast of a vid card.
Yes if he was running a P3 800 with 128 meg ram, I'd suggest spending that money elsewhere. But otherwise the system specs suggest that he'll be able to run the game just fine at 1024x768 or 1280x1024, with 256 or 512 textures, and 4x FSAA, and as long as he keeps the detail sliders down to a reasonable level, he'll get great framerates with very nice image quality.
It's always seemed to me that how far you can move the detail sliders is more dependent on cpu power than vid card power, as long as you have a reasonably modern vid card. So drop the sliders a bit (who really cares what's on the ground anyhow?), pump up the screen resolution, and run 4x or better FSAA. That gives you great framerates and a beautifully smooth image. The better the vid card, the more FSAA you can use.