I suggest starting with Yellowdog Linux 3.0 . Do NOT try the latest 4.0 as they dropped support for OldWorld systems. I had 4.0 running on my 4400/200 but the sound in 4.0 is broken on ALL PowerMacs.
Anyways, use the documentation from Yellowdog 3.0 or even 2.0 to configure BootX. Its really only a matter of installing the BootX application to a folder and then selecting a kernel to run and the proper startup ramdisk for installing whatever distro you want. I used the old Yellowdog install howto to install SuSE a long time ago on my BeigeG3. It's all the same idea.
Then you can use the "Installing on OldWorld Machines" located at http://www.ubuntulinux.org/wiki/InstallOnOldWorldMacs
If you are a Linux newbie, then I suggest Yellowdog 3.0 for that old machine. You *might* be stuck with 2.0 or Champion Server 1.2 on something that old. I couldn't get ANY version to run on my 6200CD last night (Error 10 and 2s) so I eBayed it for $1.00 and busted out my 4400/200 for YellowDog and Ubunto Linux.
Hope this sheds more light for ya. Otherwise please feel free to email me or something.