I always tell people that are new to Linux/UNIX to concentrate on learning the Shell language itself (including shell scripting).
The shell is one of the common denominators of Linux/UNIX flavors.
After that, it's just learning which apps/progs/servers do whatever it is that you are trying to accomplish (web/file server, etc..).
A monkey can learn to use a certain program in an hour, however, learning how to "glue" these programs together (using shell features) is where the magic happens.
I would suggest either going with the VMware Server on top of your existing OS, or finding an old CHEAP x86 box, and installing whatever flavor of Linux you wish to use. They all have the shell.
A good one in my opinion is CentOS, as it is almost identical to one of the most popular "enterprise" Linuxes in use today.
Also, if you are just trying to learn shell scripting, don't bother with installing any Desktop Environments or GUI programs, as they hardly apply in the "real world".
This guide right here is the Truth:
http://tldp.org/LDP/abs/abs-guide.pdf
It assumes you know nothing.
Good luck.