Compiling img files on a Mac

[cocoloco]

I have downloaded some open source maps of South East Asia as 'img' files. I'd like to put these together into one gpsmapupp.img that I can load on the SD card of my Garmin 60CSx. When I open Garmin MapInstall I get the following message:
'No Garmin Maps Found. We could not locate any Garmin map products to install. Please make sure you have a Garmin Map Product installed and run this application again.'
How can I compile these 'img' files on the Mac? Thanks!

[Indrid Cold]

It's easy as long as you have an Intel based Macintosh; install Microsoft Windows and boot into Windows with Apple's Bootcamp.