Virtualbox

[k-net2020]

As per Osborne82's Part 1 Guide https://www.digitalworldz.co.uk/index.php?threads/116910/

an excellent option is Virtualbox presently, 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.

http://www.virtualbox.org/wiki/Guest_OSes

innotek VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL).

It's FREE GPL, stable and works very well under Vista which is suprising but it's a good choice if you want to do some real Linux development under Windoze