Firmware is basicaly a patch like you would apply to a computer game or application to fix issues.
The basemap is the default map loaded on the unit, Very basic only showing major roadways and ect.
The firmware talked about above is the European release and installs the European basemap on the unit after firmware install. The Eu Firmware is nice, it seems to speed up the unit, better response, and new features.
New Features: http://www.magellangps.com/support/notes.asp?supportID=380