Microsoft Online Virtual Labs
If you haven't had a chance to try out the online labs - you should. It beats building these systems and they get updated regularly so there is always something new to try. Plus, there are two places you can go, on the TechNet virtual labs, most technologies are covered including ISA, SQL Server, MBSA, WSUS, Active Directory, SMS, Live Communication Server, RMS... and the list just keeps going. And then for developers, you get the MSDN virtual lab site too.