Question about loading a map set onto the 478. I just got from a ebay a used 478. It came with nothing battery was toast. After putting a new battery in it everything works fine. My question is, will it erase the preloaded North America City Navigator ver. 8, if I attempt to load in a few roads and recreation counties, and or if I load a gpx2img map set. If I'm not mistaken it allways says "erasing previous maps". If it does erase the preloaded City Nav, then I'm screwed because I do not have a cd....Correct??