I'd be more concerned about the machine than the OS. I doubt you'll have too much trouble getting it to run on any linux distro with a little effort but since Wein2k is closed source, for an easy install you probably want to stick with whatever platform they package their binaries for.
".deb" and ".rpm" are the most common. So I'm thinking Redhat and it's derivatives or Debian and it's derivates.
Next question. This is a fairly expensive program, even for an academic license. If you were a student I assume you would be using a free DFT package. eg http://exciting-code.org/
Since you are probably buying this for an institution it may look better on the books to buy something that will be supported such as an RHE server. Regardless you are going to want a powerful setup for DFT calculations.