That was the wrong link I'm sorry, I didn't check properly. Your etrex isn't a protected device and you only need to unlock the map img files with gimgunlock. The thread has been removed but you can get get a download from this link:
Spoiler:
[Only registered and activated users can see links. ]
Credit to member hard69

Usage: Simply drag the locked *.img file onto gimgunlock.exe and wait for a few seconds and the map will be unlocked for use in other 'unprotected' devices. Make a backup of the original map img file before you start.