I don't know the answer exactly, but see this previous post:
If I were you my first ports of call would be:
also the man pages for mouse, just incase.
It's well worth taking a look at man keyboard and XF86Config as they talk about how to assign new functions to num lock, caps lock and scroll lock (aka the led keys) and tell you how to assign their defaults.
It can be a pain in the bum trying to get this to work - expect your mouse to behave in really strange ways and remember ctrl+atl+backspace to get out of X should your mouse fail all together.