Linux is a completely free, public-domain version of Unix for PC's.
It is a FULL Unix  --  Unix kernel, shells, compilers, editors, 
X11 window system, etc.  --  everything.  There is a tremendous 
variety of software available to add to it, all free.  It can
coexist with DOS.  It also allows you to use your PC as a remote
X11 terminal to other machines via modem.

Not only does Linux provide you with great convenience, allowing
you to do your homework at home (without tying up your phone line!),
but also is an excellent chance for you to learn things about
computer systems which you will never learn in school.

You can get Linux by anonymous ftp from a number of sites around 
the country, such as sunsite.unc.edu (pub/Linux) and tsx-11.mit.edu 
(pub/linux).

Linux comes in various packages called "distributions."  I
recommend the slackware distribution.  

You can download Linux to a campus workstation which has a floppy
disk drive, and bring the disks home for installation.  Or, some
commercial businesses now sell Linux CD-ROMs.

Installation, etc., is well documented in the distributions.  And
again, the installation process itself will teach you some valuable 
real-world knowledge which you will not get from school.