Ringtones should be stored in
\Windows\Rings or
\My Documents\My Rintones.
System sounds such as Text message ringers alarm clock ringers, IM, etc. have to be stored in
\Windows
Never use ringtones stored on the storage card.
There is also a section on this forum dedicated to Ringtones
http://forum.ppcgeeks.com/forumdisplay.php?f=19