Well you could always test the memory with a free utility at
www.memtest86.com
How often do his BSODs occur? Do they seem occur at any specifiic times?... While playing games... encoding/image editing or any other system intensive operation?
I suppose if we're looking into hardware a 2nd guess for BSODs/system instability is the power supply. Whats the wattage? How old is it? Is it generic?
After looking back at that I guess its a ton of questions.. just trying to get a better idea of whats actualy happening so its easier for someone to troubleshoot