Gentoo is a fantastic distro to learn to admin a linux system. I can't think of a better way to start, to be honest, if you've some PC knowledge.
First, their forums are fantastic. I've never had a problem that they couldn't solve for me .. they are the linux equivalent of MPC, in my opinion.
Second, their documentation is second-to-none. It is fantastic and it is enough for me to recommend their distro.
Finally, the process of bringing your system from source to fully working install will teach you more about the guts of your system and linux than any other 12 hour tutorial. Do yourself a favour and build Gentoo from stage 1.
Ubuntu is great if you want to install linux and play with it .. but it is the Windows of linux. It works, it installs easily and it includes everything that you need .. but it is limited, kludgy and a huge install.
Gentoo home page
Gentoo installation guide