I just helped my friend order and build a c2d based machine, and he keeps getting random BSOD's/restarts, we've tried just about everything and still can't get the thing running, the specs are:

E4300
Asrock 4coreDUAL-VSTA (I do have the original DUAL-VSTA at my house, the older version of that board and I may give that a try tonight)
PNY GeForce 6600 PCI-e, for the AGP card we tried a Radeon 9500
3 different sets of ddr memory, both in dual channel as well as with just one stick.
420w psu, we also tried 2 bigger ones with no luck

Temps are in the 35c area

As for hard drives, we first had 2 SATA drives in RAID 0, when we got BSOD's we figured it was the SATA controller because it was acting kinda buggy in the first place, we reinstalled windows on his IDE drive, no luck.

So what happens is, when we originally assembled it, it would work for a while then randomly crash, now as soon as it gets to the desktop it locks up, sometimes it doesn't make it that far.

It does not boot into safe mode any better

I tried putting an AGP card in and it appeared to work fine the entire time we used it, the next day he told me it crashed on him :?

I'm about out of ideas here, the only thing I can come up with is an incompatibility between the PCI-e card and the board, because that board has that funny 4x electrical slot.

Any ideas? and sorry for such a long and not so well organized post

Since you've tried different power supplies, hard drives, graphics cards, and memory configurations, I would try that other motherboard.

It could be the processor. I would check to make sure that its contact points are clean on the board and on the processor.