Unix cant be got free of cost , instead u can get BSD , Linux and all those variants of unix .
I suggest BSD for u to get a closer experience like UNIX < SINCE Linux despite its popularity was made easier day by day for newbies .
For a PC there are shell program compiilers for windows platform .Try googling for that for a painless experience of scripting in unix.
The intro lessons of Unix is abt the overview of how unix functions . u can get more learning materials from unix.org / \ just google for unix .
and if its Linux > sky is the limit for materials .
there is even a special google.com/linux site functioning to search for linux oiented queries