A) read the sticky thread (the first posting on this forum)
B) go to the EDITORS DEPARTMENT of this website,
http://www.ofpec.com/editors/index.phplook at tutorials, and there are about 5-6 on custom in game music.
From the top of my head tho, here is a simply way to make your units respawn in a MULTIPLAYER MISSION (I dont think it works in single player - dont hold me to that tho)
description.ext
respawn=2;
respawndelay=5
Other than that, read all the tutorials and experiment.
Cheers
Adam