There is a java virtual machine that should work on almost all systems. Takes me forever to find it.
and you can run linux from a browser. http://jpc.sourceforge.net/tty.html
There may be other NX based systems that you could access too. I forget where they might be.
Plenty of small OS's that can run on qemu. Some are fully setup and easy to run from a flash drive.
Another way may be to use a live cd or floppy to practice. Boot computer to the OS and learn.
Another way is to use a dos based clone of linux/unix. MKT tools used to offer a neat way to run linux commands in dos.
Might install services for unix as it has almost all of the common commands.
Might move up to a live usb flash install and boot to it. See pendrivelinux.com.
There is also a cd that has cygwin from I think Indiana University. Put the cd in and you can run linux command line stuff.
As you are trying to learn I'd suggest you do not attempt to access your RH systems until you are fully trained.