I'm not familiar with the Spectra cnc upgrade. I'm guessing the Linux software would be EMC2 (
www.linuxcnc.org) which you can download along with Ubuntu Linux. I've got an old PC with Linux and EMC2 which is running a Taig mill. It works great! Ubuntu Linux should be fine for your students. If they can use Windows they should be able to use Linux.
I guess I should have asked if you wanted a plug and play solution or are you wanting to upgrade the machine yourself or as a class project.