I wanted to play around with Linux and do some testing. I've tried installing Linux on a Virtual PC (2004) guest but couldn't get it to work.
I figured with all the folks out there proselytizing about Linux maybe someone had made an guess file that I could just download and open up in Virtual PC (ideally) or VmWare.
PS - I asked question on ExpertsExchange about 2 years ago and all I got was people telling me I should use VMware (but not suggestions of where to find a pre-made Guest record.)
VMware player: http://www.vmware.com/products/player/
Vmware images: http://www.vmware.com/appliances/
The appliances website was down for me, but you can download premade images of various operating systems and run them using the vmware player or vmware server.
Ubuntu 8.04: http://www.vmware.com/appliances/directory/1224
Also, just look at the popular section on the right-hand side. I have found that when you want to use Linux, vmware is the way to go. I have had issues trying to install it on virtual pc, but that might have changed since I tried it back in 2006 with Fedora.