Win 2k can run most programs just fine and is a LOT nippier than XP, Vista is slower still, and will run like treacle on a system that runs Win 2k very well. I think that is people's biggest grief with the new OS - it should be *faster* than the old one, not slower. Just seems like they did the typical lazy PC developer thing of sloppy optimisation and just told people they need xyz new hardware.
When I run XP in an emulator, it is sloooooow. When I run Win 2K it is almost full speed, and I can run a *lot* of software in Win 2k.