[Fry]

It returns -1 if no player is found at the specified location, otherwise the player's id (I'm not absolutly sure whether it returns the level or server id, but if I remember correctly it's the server id), yes.

Ben just pointed out that level/server id might be confused with an id for a level/server or stuff, the correct names would be id for the player number for the entire server, and index for the player number local to the level. Although I consider these even more confusing.