hi i am an idiot: how do i install this game to use in Boxer on my mac?

If you have GOG's exe you first need to run the installer in a Windows environment or WINE to unpack the installer contents. Then you can either run the DOS installer inside of Boxer by simply dragging the game's folder onto Boxer's "import a new game" icon or a lot of times literally just copy and paste the folder into Boxer's DOS games folder. Rampancy has a thread about getting GOG games installed on a Mac in general.
(http://www.gog.com/en/forum/general/gog_games_on_mac_os_x_a_how_to)