Again, here are the original sound files so you could compare them with what you hear:
http://shoutbox.menthix.net/attachment.php?tid=9391&pid=69806
(Sounds.zip, 120 KB)
DawsonsFreak, if you don't have the "Send Command -> Sounds" menu then you have an old version of Messenger Plus!. This is a very common problem, you have to download Plus! again, try a different mirror:
http://sock.demon.co.il/mp2
Edit: Oh and yes, all the sounds still work fine with this version.