I have been playing w/ VMWare Fusion (for Mac OS X) and VMWare Server (for Windows) over the weekend, and now have a couple of FreeBSD virtual servers running on my iMac and my X40 (both with 1.5GB RAM). This provides a server environment virtually identical to our production server facility, for use as a self-contained development server on-the-go, even where there is no network.
Performance of the virtual server on the iMac (dual core) is very good. The X40 is a much slower machine, so setting the virtual server up to a useful state takes much longer althou once this is done the whole thing is very usable.
VMWare Fusion is USD80. VMWare Server is free (as in beer). I’ll play some more and verify that the virtual machines created under one environment is compatible with the other.