I'm still running XP on a now 8year old full size tower kit, with a 1.6ghz AMD chip. All I do on it is internet stuff anyways.
My wife has a 14month old laptop that wouldn't work with Vista hardly at all, so we put Ubuntu on it. That thing is so amazingly fast now, it's unreal. No garbage to bog it down.
If you're leaning towards an anti-Windows mentality, go Linux. You can then be a real hippie instead of the hippie with a trust fund and an Apple.