Sorry, I didn't make it clear: mucking around in the BIOS didn't help me at all (except insofar as sorting out the RAID configuration - but that's another story). The issue with mine was that having a USB keyboard/mouse instead of PS/2 caused the system to hang for no obvious reason after very little time, quite erratically. Some USB devices are okay plugged in, some aren't. From checking out hardware discussion forums I found out that changing the USB Legacy setting in BIOS helped some people, while others just ended up having to unplug everything from their USB ports.
It might not be the USB thing at all. Essentially the 965 chipset is still immature, so some people get on fine with it and others experience bizarre and often inexplicable problems. As I said, BIOS and chipset driver updates are being released all the time for most 965 motherboards (I'm still awaiting a driver update for my Gigabyte P965-DS4 to fix this DVD-playing issue!), so keep checking the manufacturer's site. You could check your RAM (remove/swap modules) to see if it's a memory issue, as that can sometimes come up, and you should probably also try removing all unnecessary hardware from your rig before installing to see if there's a conflict, but this sort of problem is the worst to diagnose. I only mention USB devices as this is a particular example of my own experience with the 965.
As for OEM discs being bad: almost never. It can happen, but usually as a result of damage or warping in transit. OEM disks tend to be "stamped" rather than burned, in controlled conditions, and you're just as likely to buy a brand-new non-playing audio CD as you are to get a faulty OEM disc. If it's bothering you, try using a live-linux disc to boot your system. If you have no problems with that then it may well be your disc, but I'm very doubtful.