this is what i know.
i am running vista RC2 and am having no problems. its not slow at all and i have no preformance issues.
here are my specs on my notebook which i've had for over a year now.
inspiron 9300 (2gig and its not dual core either), 2gig ram, nvidia go 6800,100gig hard drive
no sluggish behaviour, i can play all the dvds i have without any problems. the only thing is that having the sidebar open uses up like 10megs of ram but apart from that, the OS is snappy...