The website linked to by pfr indicates that the system can be run on a USB key, ie without installation on your hard drive. Why not just try it and see how you like it? Live DVD is another possibility, but IMO gives only a rather poor idea due to repeated pauses for reading the disc.
Running from a key is a slower and less satisfactory process (than a full HD install) in my experience, but it does give a good idea whether a particular distribution plays nicely with your hardware, and will give you a chance to try out any more specialist software included. If you like what you find then actual installation becomes so much more worth the bother.
This has all strayed rather from the initial purpose of the thread. At some point I have a couple of Win7 upgrades to carry out (not looking forward to that) but I suspect they will be the last for me. I am finding I can do more without Microsoft, and I don't really like the direction they are taking their systems.