Branch Server Exchange Clients

I have recently set up a seperate server 2003 DC in a seperate branch office. The DC is connecting to my main server by VPN and everything is working well. Emails are coming from exchange, Im able to access shared files from the main server, DNS resolutions seem to be working.

I set up a DHCP server on the box allowing clients to access the network via the server. I was hoping that the clients would be able to access exchange but they cannot. They also cannot access the remote servers files via a dns entry e.g. \\server\files

Im sure its got something to do with my dns setup but I cant see what Ive done wrong. Why does the VPN connection stop at the server? why cant it reach my clients so that I can access exchange.

Thanks