So it turns out that the board supports up to six channel audio, and I just never noticed the additional audio jacks before complaining about the sound problems. An idiot is me. Still, it's not all my fault.

Pretty much what it says. So, I got my brother’s old PC, and I’ve been spending most of my waking time getting Vista and various programs installed and happy. Unfortunately I’ve hit on a major stumbling block. The motherboard has no official Vista support (and indeed is out of manufacturer support) and there’s no working, usable audio.