Did you do a fresh install the 2nd time as well when all these problems occured?
Have you tried to insert your XP disc in and fix the MBR?
I do know that Vista 32 Bit max RAM it can handle is 4GB. It could also be your mobo drivers. Best bet is to try again. Hopefully things will work out better for you. Just when installing Vista make sure that you format the drive first during setup.