Yes, just press the little sound icon, then press "Add/Edit/Remove Sounds" , then press "Add New Sounds", then press next if the "Create a sound from an existing source/music file", browse for the file, and let it encode it properly, then you have to choose the 0-10 seconds that you want to be playing as the custom sound...
You can only have 0-10 seconds because of Copyright purpouses.
