Depends on what you'll be using the system for. The two heaviest things I've thrown at it were GTA3:VC and video crunching. It handles GTA3:VC just fine. The video crunching lacks compared to faster systems (of course) but it's way, way faster than my current main system 2x533MHz Celerons. If you're not going for absolute performance, pocket the extra bucks or buy more gadgets and take the Athlon.
I've been impatiently waiting for cheapish dually Athlon 64s and of course 64bit Windows...