I'll make the generic recommendation for Knoppix. Get the .iso from
Distrowatch.com. It boots and runs entirely off a cd. No install, no configuration really, just put it in and reboot. It really couldn't be easier. I've used it on a couple of different computers with very different components, and it auto-detected all the hardware perfectly. Also, since you're running off a CD and ramdisk, you can do anything you want and not worry about messing stuff up. Deleted your kernel? Just reboot. Lost KDE? Reboot.
It's what I'm using to learn until I have time to get SuSE up and running in a few days. Then I'll be off to Debian and (maybe someday) Gentoo.