if you want to learn Linux, try reading "Unix basics" first or "Unix for beginners".
It will also help if you have a Linux machine in front of you while reading Unix basics and it will help if you will "not" use GUI's on your Linux machine while trying to learn Unix basics.
Once you have the grasp of the basics of Unix (e.g. mount points, devices, file systems, run levels) try to install a Linux box from the ground up.
if you have a Mac OS X, you can use that as a reference by working on the terminal. Mac OS X and Linux, although different, have a lot of similarities as far as the basic OS structure is concerned.
Linux is fun, with a lot of different flavors and it's free!