I would figure that "both" computers simply don't have enough a** to run Vista properly. Average PCs haven't been ready for prime time in running Vista until around late 2007 or early 2008, so anything older than that will probably stumble on Vista. Best suggestions I could offer would to uncheck your System Restore and stop-then-disable Superfetch and Readyboost in Adminstrative Tools/Services located in your Control Panel. I anticipate another poster coming along and saying, "Shut down Superfetch? Are you stupid or something?" You know, as if the free world is fully dependent on that bell-and-whistle piece of unnecessary Vista dung.