I have a MacBook Pro with VMware Fusion install. Fortunately, because of the cost of a laboratory with 4 or 5 servers, this setup works for me. I have various virtual appliances include Windows 2008, Ubuntu server, Windows XP, Backtrack, and others. Today I am working on exploiting the Ubuntu server with Backtrack 4 in the virtual environment.
On the fly, I configured eth0 interfaces to be on a class B network with the following linux commands:
Ubuntu Server
# ifconfig eth0 inet 10.10.73.54 netmask 255.255.0.0
Backtrack 4 Server
# ifconfig eth0 inet 10.10.74.54 netmask 255.255.0.0
Once the host are recycled, the TCP/IP configuration will revert to the original settings.