For people who are trying to learn about windows enterprise administration that would like to create a virtual lab, complete with virtual routers to play with ideas like managing trusts and other things (like migrations) between two forests, you can view this video to learn how to use ESX with Vyatta to create virtual networks to separate them on.
http://happyrouter.com/running-a-virtual-router-firewall-inside-vmware-esx-with-vyattaRemember, practice makes perfect!
Also, don't ask me how to do this or how well it works. I don't have the hardware to run things like this, I just thought it would be a great idea.