I have a c550 and I didn't get any discs or backup stuff with it either when I got it. I did though save a backup of the device before adding updates to it incase I ever needed it. Luckily I did though cause my computer shut down or locked up one time updating it and even though I had removed the bad map, it still thought it was on there so I never had room to install the good map.
Looks to me though, you have 2 options maybe. If all you messed up was the map structure, maybe you could load the maps to an sd card and run the system that way? Also, maybe find somebody on here with a c580 willing to help you out, format your garmin, have them send you all the files from the garmin directory except the map image files(ex. gmapprom.img, gmapprom.sum and gmapprom.unl) and load them to your directory, and then you go out and load your own map image to it. I really think this would work and on mine, those files are about 400 mb's so that would be a lot easier for somebody to send or upload to a site for you to download than say 2 gb's.
Here's is my problem! I have Garmin Streetpilot C550. Last year I tried to update the map. When process stop working. The unit works only because I
save the map to the sd card. When trying to delete the old file from unit it deletes it! But when you go back it is still there. And when I try to write the file from the sd card it says disk is full! So its a 2 gb, Used 1.46 gb Free 495mb. So what do I need to do to update it with out saying disk is full. Any in put on this?