have you tried adding /3GB extension to the last line of your boot.ini file?
My system was really unstable (similar to yours) and now after adding this it works well.
I have XP not Vista 32 so it may pay to check first before doing. Also backup your existing file before changing.
Example below from my boot.ini
multi(0)disk(0)rdisk(0)partition(1)WINDOWS=”Microsoft Windows XP Professional” /noexecute=optin /fastdetect /3GB
cheers
Lance