If you have problems with the installer try this:
install Mapsource last version,patch it, transfer from the other pc ,where your map is installed properly ,the CNE gmap folder you find in :
(in XP - C:\Documents and Settings\All Users\Application Data\GARMIN\Maps) or
(in Vista, Windows 7 - C:\ProgramData\Garmin\Maps)
run in it this tool
[Only registered and activated users can see links. ]
the map is big it will need some minutes-
I think it will solve your problems