EDIT: Unless your vendor says they're not ready for version X, I wouldn't recommend buying the older versions. You will want the enhancements and bug fixes the newer software has. You should also consider buying from reputable sources and not just random cheap sites via Google searches. There are a lot of rape sites with counterfeit software. Plus, since you're describing multiple desktops and servers in your business already, you should investigate Microsoft Volume Licensing programs. You'll get better pricing under a volume license program.