Logging onto single domain across ipsec tunnel

I have a company with 2 office about 20 miles apart, both have netopia dsl models connected to each other via an IPsec tunnel. the main office has the 2003 server and 2000 terminal server and exchange server, the other office has the netopia, and a hub with all the computers connected. Currently everyone in the 2nd office used terminal services to log onto the server.

Is there a way to have them logon to the domain controller at the main office without having to use terminal services since we have an IPSec setup?

Thanks
Brandon