The LiveCD is nice, although you might be limited in "learning" because you won't be able to write to the part of the filesystem that has the distro files on it (cuz they're on the CD).
Some other options might be... using MacBochs or QEmu, although these will be crazy slow. I got DSL running on QEmu, but I could not get Slax running, which is too sad, because I wanted to try Wine under Slax. They are both much slower than VPC, sadly.
Finally, if you're on Panther, on off chance, you can use
MacOnMac to run a PPC Linux distro in a virtual environment -- you will be able to write to the mounted disk image, but won't have to repartition, and you'll have relatively close to native speed this way.
🙂 The only sad thing is that MacOnMac development doesn't seem to be very fast-paced at the moment. The site hasn't been updated since around when Tiger came out, and it is not Tiger compatible. (FWIW, MacOnMac is a derivative of MacOnLinux, which can be used to run the MacOS in a virtual environment on top of PPC Linux on Mac hardware.)