I'd think that Ubuntu would be a good place to start as well. I would like to mention that you don't have to repartition anything if you would simply like to try it out. First step is downloading the iso and either setting it up to boot from a flash drive or burn it to a CD.
I believe their is a way to run Ubuntu from within Windows, but I've never done this before
The next option would be to simply run from the bootable flash drive or CD. This will give you the full un-updated OS to explore and checkout.
Once and/or if you still want to install, Ubuntu is actually pretty good with walking people through the repartitioning process. There is a neat little guide on the download page actually, that you can view by clicking the "show me how" buttons; which explains this more simply than I could. I suggest looking over that and booting into it, then post back here if you have any other questions! It will warn you before doing anything that has a chance of loosing your data
A quick googling has brought up this guide, which looks to go over the process pretty well. Once again, do ask if you have anymore questions!
http://www.psychocats.net/ubuntu/installingEdited by Fir3Chi3f - 3/11/12 at 9:33pm