To use winterboard to have custom tone go to cydia. Look at catagories and look for ringtones or system sounds. (if that doesn't wok search SMS) once you download it, go into winterboard and it will have it listed. Then just check it and let it respring. Then when you go to 'new SMS tone' everything is that ringtone. Some ringtones on cydia actually go straight into ringtone. But to use your custom ones I'm not sure how to do that. Look for videos on YouTube. You'll have to do some SSH'ing though.