Test domains for trust relationships

Hi, I have to set up two testing domains for a client so the person can test/learn about trust relationships. One small network is in place already – nt4.0, pdc and two clients – runs wins, dhcp and dns. Clients are attached to the pdc via a 100mbpshub. The second domain will consist only of a PDC. what is the easiest way to connect the two domains so the client can explore trust relationships (let me add that the client has done a bit of experimenting and has damaged the dhcp installation on the one network so I want to make this a straightforward operation for the person). Thanks in advance.