Windows NT on FreeBSD
FreeBSD is my operating system of choice. I'd run FreeBSD as a guest operating system using VMWare and Windows XP as the host OS. Yesterday I managed to do nearly the oppositive. I installed VMWare via the VMWare3 port on my Thinkpad a20p running FreeBSD 5.1, and ran Windows NT 4 within VMWare!
Essentially I installed the port, started vmware.sh, and created a /usr/lib/vmware/licenses/user directory with the license.ws.3.0 file in it. I also executed 'mount_linprocfs linproc /compat/linux/proc' to prepare the Linux emulator. I used an unused VMWare 3 license made obsolete by my VMWare 4 license, and fired it up. Unfortunately, I had trouble getting the network to work (and read in the mailing list this is common), and read only one guest OS per session is allowed. I plan to use Linux as the host OS for my next test.