In my own opinion, worth as much as it may be, the best way to learn basic administration is to run a Linux system yourself. I'm not saying to wipe your entire hard drive immediately and install over whatever Windows version you are using, but I do suggest you at least run a LiveCD regularly and maybe even install as a second operating system.
Work with it for some tasks, become comfortable with using the command-line and using the package manager that comes with your distro. Read a little bit about the kernel (nothing too in-depth of course, but even just the basic structure of how kernel modules are used), experiment with the different filesystems. Install and configure a LAMP (Linux, Apache, MySQL, PHP) stack (or use PostgreSQL if you prefer) and install various web applications.
If you really want to learn, teach yourself shell and Perl scripting. Those two are sort of the . . . "swiss army knives" of UNIX-derived systems.
I would write more, but I'm afraid that I need to get somewhere in the next three minutes. I wish you best of luck on your journey, however you wish to take it. You'll be frustrated, exasperated, and even angry at times, but . . . well.
It'll be fun.