Many of these tips were found on the gpspassion forums. c320/c330 Hints: Software Updates: The system comes with a map of CDs and some basic transfer software.
The c320 system is a little cheaper and uses SD cards. Both these units rock, have many features, are frequently updated, and are rather inexpensive now.
I believe you are stuck since Garmin no longer updates maps in the old format.
I figured the map format changed, not sure when since it updated in January 2012.
Press and hold the bottom right hand corner of the screen. Turn the GPS on (and continue to hold the right hand corner). A warning screen will appear and ask if you want to continue. This is excellent after buying a used unit or after moving to clear all your data.
When asked to enter a house number, just click Done.