O.K., I think a may have it now....
Unit ID- Can be found in the GPS menu's: Configure> System > System Information
Using this and the Map ID (411), I can generate a 25 digit unlock key. Using Notepad, copy the 25 digit key into notepad and "Save As" "gmapsupp.unl". Create a directory on the SD card called "Garmin" and copy the file "gmapsupp.unl" and the locked map file "gmapsupp.img" to that directory on the SD card.
Does it matter if the file names are upper or lower case?
I can't try it till tomorrow. Is this correct ? any comments ?