I tested the memory out with a friend’s motherboard, which happens to be the exact same model. The RAM worked fine. So I swapped my memory for a 2GB stick instead; now I have 2x2GB sticks giving me 4GB of RAM, but still single channel. And my motherboard is apparently incapable of handling more.
I am considering getting a new board and dumping this one completely – I’ve just had too many problems with it (this is the second one, and both have had issues with sound, USB, hard drive, and now memory). I certainly can’t recommend it.
However, I have four PATA devices – three hard disks and a DVD writer. Most motherboards these days only have one PATA controller (which supports two devices) and maybe 4-6 SATA ports. I could replace the DVD writer with a SATA one, and I suppose get an external enclosure for one of the hard disks (it’s only used for backup). Or dump / sell it and get a new SATA hard disk (it’s a 350gb drive).