Window Server 2003 trust setup

I have two locations with window server 2003 setup with two different domains name. I would like to access both domains from anyone of the location.
What do I need to do to get this establish.

From my xp pro desktop I created a vpn and was able to access the servers but how do I do this with window 2003 server.
How do i establish a trust relationship between two domains in different location?