Okay few questions.
Did you oc the cpu and ram separately to find their max oc individually or did you just start to up the HTT bus?
Have you changed your ram timings, voltages, and dividers?
Have you taken as much load off the chipset as possible by disabling unused things such as a floppy drive, firewire, extra usb ports ect.?
So not to leave you with no help and only more questions I'm gonna assume some answers to those questions and maybe give you some help.
I bet you just started by upping the voltages and htt bus speed and that is most of how you overclock but you need to tweak your bios so that other parts can handle that. First I would look at your memory dividers and adjust them so your ram is running
below their speed rating.
That will hopefully eliminate the ram as the cause and you should also make the timings kinda loose too just to make sure.
next is the chipset load. the chipset handles all those bells and whistles on your mobo, so to lessen the load on the chipset disable every bell and whistle you dont use. then bump up the voltage to it a small amount to give it some more stability.
I know this article is getting dated but you should find some useful information to give you a good starting point. It’s not for x2's but many basic principals should still hold true.
short media guide to oc 939 and 754