Did a bit of digging, but didn't really find the documentation I need for this. Hopefully I didn't just miss something really obvious (and if I did, it's fodder for the MAME FAQ at least, right?)

How exactly does MAME's MIDI output work? How can I direct it to a Windows MIDI device so that I can have a MT-32 hooked up to my virtual machine?

I've been looking at this in QMC2 and I've got a Sound Blaster hooked up and a midi port attached as a result, but I'm not sure what to do next.