I have a custom sound that I want to use as a notification sound. I can find the sound in the ringtones, but I don't know how to get it into the notification sounds.
Put it on your SDCARD in the folder /Media/Audio/Notifications/ and reboot your phone. If the folder doesn't exist, just create it. Also, besides /Notifications, you can have folders for /Alarms and /Ringtones in the /Media/Audio/ folder too.