Clarifications:
By last a while, I mean 1 year, which I suppose isn't that long, and it doesn't need to be upgradeable after that (for reasons). So if a 2.5-6GHz XP is going to be able to handle all the new games in the next year or so (D3, STALKER, etc) without holding back the 6800U I would want to go with that. If on the other hand the 9800 Pro isn't going to be able to handle any newer games without great graphics quality/FPS I'd want the 6800U.
Great graphics quality = 1280x1024x32 all eye candy.
Great FPS 45-60.
I'm thinking the 6800U since I'm not sure that the 9800 Pro would be able to handle all that with new games, but I could be wrong. Also I suppose there's another option of a 6800GT/9800XT and a slower CPU than the 64 3200, but if the XP-M is going to be equal to the 64 3200 I don't know why I'd bother. What sort of overclocks are people getting with the 64 3000/3200s anyway?