Test Network with Internet Access, but no access to anything else

I'm trying to setup a test network in a domain environment with one VM that has Windows SBS 2011 Essentials and two VM's (Windows XP and Windows 7).  I want to create a domain environment for the three and have them have access to the Internet, but not sure the proper way so it doesn't effect my current setup.

I have a domain environment with a server running as the DHCP/DNS, etc and a bunch of VM's.

What is the proper way to do this if I turn on DHCP and DNS on the SBS 2011 server and it not effecting my production environment?

I'm currently using Workstation 8.