.....But really, I think all this tech info is going beyond what's appropriate for Garmin's forums. I suggest you join in the fun over at GPSfileDepot to discuss mapmaking issues.
I'm still surprised Garmin doesn't include an "image import" function to work with unprotected .img files that don't have installers!
Well, on the Mac they do - it's a program called MapManager. No such thing on Windows though. I suspect that's because they got a clean start on the Mac just a couple years ago, but Windows already had it's "tradition" of registry based maps, and it was only intended to work with their own products.