copy gmap folder in:
(in XP - C:\Documents and Settings\All Users\Application Data\GARMIN\Maps)
(in Vista, Windows 7 - C:\ProgramData\Garmin\Maps)
You'll have your map in Mapsource. Nothing to install, nothing to split. Just unlock it if it's not already unlocked.
Select map tiles you need in Mapsource and send them to device by "send to device" tool