Trusting relationship

Hallo everybody.
I’m in the need to establish a trusting relationship between two NT domanins that are placed in two different places. Between the to building there is a VPN. The two domains are placed in two LAN with different IP Address. I have to permit to my user in place 1 to retrieve drawings from a folder on the NTserver in place 2.
I tried using the function in “User Manager for Domains” but it seems that the two domains name are not recognized. From place 1 I can see the server in place 2 (using Find Computer, asking for its IP Address).
Any clues?
Thanks a lot.
Andy