If you don’t want to crate your own Garmin maps, download one of the precompiled IMG-Files (http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/Download) and save it to the Garmin-Folder on your SD-Card. That’s it. There might be some additional steps necessary like unzipping the downloaded IMG-File or creating a folder named “garmin” on the SD-Card…
did http://garmin.na1400.info/routable.php work for you? I’ve been using them for several months now with few complaints. I have an Oregon 400t. If you are still having difficulty I can help.