This is cool stuff (not that I'm the first to find it!) - VMWare

It allows you to run virtual computers from windows or linux. At the moment my PC is dual boot Debian linux and W2K, and if I need to try something out on the other OS I have to reboot. Now that's a thing of the past! Well, more or less anyway. I found a few links to hack around with it, and was able to make my own Debian images.

How useful is it? For me I need to do lots of testing on both linux and windows, so it's great for me. Also for any web development it's useful to see results in browsers under different OS's quickly, although I'm going to need a mac image to be really useful for that.