There is a map for battery on the actual CD, but it isn't synched with GM. So when GM says play the snare, it does some crazy shit like play the splash...
Yeah the mapping regime is consistent accross all the preset kits they start you with. I wouldn't have the first clue on how to create the map myself though, as I'm pretty new to all this stuff.
I made my own mappings by hand. The Best way is to load the kit and everything... go into the drum editor in cubase and then add hits to each track until you figure out what each one is for then change the name of that track to thr relevant instrument. Then match them up.