Remove 2gigs of your ram and see if that helps. If not, reinstall Vista with just 2gigs of ram intalled and check for stability. If all is well, reinstall the rest of your ram and you should be fine.
1 320GB Seagate SATA
1 250GB Western Digital SATA
1 200GB Maxtor SATA
2x160GB Western Digitals SATA
1 320GB Seagate External
1 120GB Western Digital External
1 80GB Westen Digital External
1 4GB Crucial Flash Drive for Ready Boost
PSU
600watt Fortron Source
Case
Antec
Cooling
Fresh Air
Mouse
Razer Diamondback
Keyboard
Microsoft Natural Ergonamic 4000
Other Info
My main rig runs Vista Ultimate or Server 2008. Depending on which Acronis image I decide to load.