Steps to debug memory/motherboard (Via VB8001) problem

I have a Via VB8001 running 8.0-CURRENT using ZFS on a pair of SATA
drives.

It has two memory slots, and I have 2x2GB of Kingston PC2 5300 memory
(KVR667D2N5K2/4G) that I think is correct.

I can run with either of the DIMMs in the first slot and am able to
build and install world and kernel.

If I populate both slots then I can run for a bit (e.g. make
buildkernel) before I end up in the debugger or with the build bombing
out with a message about "bad address".

This happens no matter which DIMM is in which slot.

With both DIMMs installed the system only reports 3GB to the BIOS and
to FreeBSD, others have reported this and it seems to be a limitation
of the BIOS and the integrated video.

The fact that the DIMMs work in isolation and I have problems
independent of which one goes in which slot suggests that the problem
is either:

 a) with the motherboard

 b) with how -CURRENT sets up or drives the hardware.

 c) bad memory that only shows up when both DIMMs are in use.

I didn't get the RAM and the board from the same vendor, so I'm kind
of expecting some finger pointing.

Left to my own devices, I'd blame the motherboard and try to get it
swapped.

Is it more likely to be a memory problem?  A -CURRENT problem?

Thanks,

g.