It can support  more than one AD as long as the additional domains have
trusts to the domain that the MOSS servers are in.

There is no how, it just works. There are some STSADM operations that
let you control how names are displayed in the people picker. You might
want to check that out.

If you don't mind a little dev work, you can wire up Zones to another
authentication provider as well. It would require a custom
authentication provider via FBA.

Alright so i was on the right track. I was thinking as long as the
ADs have trust setup, they should work without any additional effort.