Legally?
How do get that

Most universities offer free enterprise-licensed software (standard stuff like Windows, Office, Mathematica, etc.) to students, if only to stop piracy. Most private ones anyway, I can't speak for state schools. I've also had enterprise copies of XP Pro, Office, and antivirus from my dad's work for years.

I could have just been a bitch and said Linux

Are you possibly referring to MSDN Academic Alliance?

http://msdn.microsoft.com/en-us/academic/default.aspx

That's what I use. Only someone enrolled in CSC or ECE classes can gain access to it (at my college). You also are "required" to uninstall it after you've finished the class, and only use it for class purposes.

It depends on how they have it set up. It can be set up so that they have a certain number of copies of installation media and only as many installations are allowed as the number of discs, thus having a limit on the number of people who can use it, IIRC.

As far as subscriptions that are set up where the school gives out user names/passwords to students to access it to get product keys and download CD images or purchase installation media, the keys and installation media are yours to keep. There is some kind of limit to how many accounts can be active at a time per subscription.

My highschool had MSDNAA. ;o It was neat.