Well you should learn what system administrators do (or might do).
http://en.wikipedia.org/wiki/System_administrator said:
The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects, supervising or training computer operators, and being the consultant for computer problems beyond the knowledge of technical support staff. A System Administrator must demonstrate a blend of technical skills and responsibility.
Read these following links (They're from people who work as system admins)
http://www.careers.g...B7-EDF0B880842B
http://www.careers.g...08-801F074320D6
http://www.careers.g...A6-287912BD5945
For the networking side of things, you should learn how various networking protocols work (like FTP, SSL, UDP...), how networking works and if possible set up home networks.
I don't know about ebooks but you should check the computer section of a local public library.
I also want to be a system admin, hope this post helps