Tool to automatically install a macro + button on 200+ instances ofexcel?

[cmotes]

I need to install a macro on 200+ instances of excel with as little
pain to each of those 200+ users as possible.

Details:
+ The macro is already written
+ I need to make the macro accessible via a button on toolbar that is
loaded every time excel opens
+ The users who will be installing this will not even know what a
macro is. this needs to be as simple as possible.

Any suggestions appreciated!