WindowsStar said:
You most likely have a MAK key with a number of installs attached to it but, since you are re-image classroom machines those are the same hardware over and over and should not be an issue and do not count against your install number. That is good to know that re-imaging is working correctly. We have not had to re-image any Windows 7 machines so far.
YEs, we have a MAK key thru MSDNAA. We have one room now that gets re-imaged weekly due to a class using WinVista and another in that same room using Win7.

We switch to Win7 on all classroom and admin PCs completley for Fall 2010 semester.