Alan:
I think Garmin does not want to get into producing a Mac OS version of the MapSource application because they don't want to just port the application over to the Mac OS, if they did do it, they would want to do a decent job, and this would require about 5 to 8 full time employees to support the Mac platform and the ongoing revisions needed to keep the application current. Keep in mind that MapSource is a monster application that has to be compatible with about 80 different GPSR's.
Salaries, overheads, and equipment to support this would probably run to about USD 1.5 to 2 million a year - and there is just no economic benefit to doing this. Although the Mac has a dedicated home user community, the bulk of the Mac's installed today are in business applications - primarily graphics. Back in the 1980's, I used to develop software for the Mac, so I have a soft spot for it - I still have my Lisa in one corner of my basement, and it still works (though I don't use it). I got out of Macs and went over to the Wintel platform around the time of Mac OS 6.3, when I saw the handwriting on the wall.
I know of some Mac users who run MapSource in emulation (under Virtual PC) on their Macs. This configuration runs well, but it is fidgety to configure the communication port to download map segments. Route and waypoint uploads and downloads seem to be trouble-free. I have set a few friends up this way.
Best suggestion I have for you is to try and buy an old DOS box (a 486 or similar) for a hundred bucks or so at a garage sale - all you need is the monitor, keyboard, and processor - you can then use this for map segment uploads/downloads, and run MapSource under emulation on your Mac for route creation and route/waypoint transfers. Or, just install your cartography on a neighbor's PC, and for the odd time you need to transfer maps, use that machine. I am pretty sure the licence agreement allows you to do that.
NB that if you save a MapSource file to a floppy when running MapSource under Virtual PC emulation, you can use that same floppy without modification in the DOS box to pull up the map segments you want. In other words, you can do everything you want to do, except map segment transfer, from your Mac.
PanEuropean