I've been messing around in Mega Man 2 some more, and I've found out a few things about the music data:

30E39 seems to be the tempo of the main channels for Wood Man's stage.
30FAE may be the tempo of the triangle channel for Wood Man's stage.
The actual music part of Wood Man's music starts around 30E3D.
Crash Man's music starts around 31280, but most of my edits to that and the surrounding values crash (pun intended) the game.
(all addresses in hex)

That's all I've managed to figure out so far, but I figure with this many MM2 hacks floating around the internet, there must be somebody who knows what they're doing. I certainly don't. XD

I'm not asking for a step-by-step guide, but if somebody could at least tell me where each song begins, that would make figuring this stuff out a lot easier.