Looks like you've done a pretty comprehensive job of troubleshooting this. I would try resetting the PMU. You might also want to connect to another Mac via firewire and boot to that machine's hard drive using target mode, as a means of 100% ruling out your hard drive. If it works fine running on a remote hard drive, then yours is the problem, and if it still gets the errors, then you know your hard drive is good.
I would leave one RAM slot empty, and then the other, in order to troubleshoot the possibility of a bad RAM slot. I would also remove the battery and Airport while doing all this, just to simplify the situation and rule out all extraneous elements.
Anyway, it does sound like the board, but testing the memory slots is worth a try if you haven't already.
Good luck!