Running the .msi only installs the gmap folder on your computer. It cannot be used to install image files. You do not even need to run the .msi for MapSource & BaseCamp any case, you can simply drop the gmap folder in the correct place and MS & BC will find it:
In Windows XP - C:\Documents and Settings\All Users\Application Data\GARMIN\Maps.
In Vista, Windows 7 - C:\ProgramData\Garmin\Maps.
You can use GMapTool to install a simple preview map in MapSource to use for browsing, but it will be useless to use for transferring an image to your device because it will lack search capabilities: [Only registered and activated users can see links. ].