Another route to getting Mapsource

Pun intended. Here's a link to a procedure that may let you install the Mapsource update:
http://freegeographytools.com/2007/garmin-mapsource-for-free

It only involves downloading and installing files that Garmin makes available for free. I have not tried it (in my case, a modification to the registry convinced the update file that it should install), so I can't promise it works. But it doesn't look like it could do any harm.