Having used VMWare to build virtual OS systems on one PC (mainly for testing applications), I wondered if there was a open source (and free) equivalent.
I found VirtualBox. It looks to do exactly the same thing as VMWare, and can be installed on a variety of platforms. VirtualBox runs on Windows, Linux, Macintosh and OpenSolaris hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista), DOS/Windows 3.x, Linux (2.4 and 2.6), and OpenBSD.
I haven’t yet tried it but would be interested in any comments or opinions from anyone that has.