I have heard that Windows Vista Enterprise MAK keys will work with Windows 7 Enterprise, did anyone tried it.
It is possible with a "frankenbuild" configuration (e.g. using some key files from Vista and replacing their Win7 counterparts within your Win7 install), but for everyday computing I highly advise against it, as if you run Windows Update, Windows Update will then "think" your PC is running Vista...and that can be troublesome. You are better off trying any other method available to you, as you risk the security of your PC disabling Windows Update...
...well, just go on and tell him how to do it why don't ya, then recommend that he doesn't... Now he has probably gotta try it just 'cuz he knows how to do it now...