On your SD card look for a folder called "Media". Inside will be a folder for "Audio" and inside that "Alarms", "Notifications", and "Ringtones". Copy your ringtones to the "Ringtones" folder and it should show up. Similarly, if you copy audio files to "Notifications" or "Alarms" they'll show up in the appropriate places as well. It must be a supported format. I know .ogg, .mp3, and .mid will work. Not sure about others though I suspect unprotected aac and wma will also work.