I dragged an AAC file to ~/Library/Sounds and launched iCal. To my horror, the sound that I put in there didn't appear in the pop-up list of alarm sounds. "Okay," I thought, "maybe it's expecting an AIFF file."
Not having an AIFF lying around on my new machine, I decided to rename the AAC file to have a AIFF extension. Magically, the sound appeared in the alarm settings dialog, but I didn't expect it to play. Guess what? It did!

