"RAM - wrong RAM can cause instability. "Wrong" can actually be "too fast". Kingston DDR-333 and DDR-400 is reported to work well. I have Geil, and may have stability issues because of that"
Also this may sound weird, but make sure you have the stock cooler on correctly. He had his on backwards once and the heat safety kicked in and kept the thing from burning up. He still has heat problems with the stock cooler. Also, if I recall, a firmware update helped with some stability issues if they have not been done yet.
I hope this helps.
~DW