Linux

There's no software. Because there are so many Unix variants out there such as AIX, Solaris, Linux, BSD, etc.
The best place to learn would be www.ugu.com, and based on what you want to learn first, there're plenty of documentation for each of field you want to learn there.
Have fun.

I think the best software are the distributions of Unices. And the best way to learn the system is to install it and try to use in the areas you want to use it. There is a lot of Unices and you'll have to choose some (if haven't chosen yet). I advice you to try www.freebsd.org
Hope this will help you

Hi !

You can find lecture materials about UNIX on Internet (go AltaVista.com and type in query string "UNIX for beginners", "UNIX administration guidelines" etc). There are some printed books (visit amazon.com for example).
But learning UNIX only "in theory" is not good idea, you need some practice. You can telnet to cyberspace.org and get account to work with UNIX (SunOS). In additional, you will get alternative e-mail address.
To receive your own account, telnet to cyberspace.org and login as "newuser" (password not needed). Then, answer few question and enjoy :)

With best regards,
Vlad.
mailto:hugevlad@yahoo.com