funny , I just did this last night. It's pretty simple and doesn't require any extra scripting, just a zone to place.
*first off place a sound zone where you want it.
then rightclick it and change this propperty-
-Sound0 (direct it to the sound you want to play)
it should already be set up to play the sound just once when the player walks over it. Check your manual, it's in there, or get the NickyDudes guide from the sticky above. It will save you a lot of time.
as for the charachter I'll leave that to someone else since I have no idea.