I had the same problem, when i installed vista it wouldnt load up past the splash screen, if it did after several restarts it wouldnt shut down. The problem turned out to be my ram, i tried all the memtests which didnt report any errors, but when i removed 2 sticks of ram (2 x 1gig) and replaced them with 2 x 512 the system is running without a problem, i am now down to 2gig rather than 3 but i can live with that if it cured the problem.
