Okay, so far I think what HellsPanda said is the best way to send emotes with the current script.
You ask one of the players to emote whatever atmosphere your trying to make.
Given that there is a player willing to sacrifice his own RP for the sake of your emotes.
I also understand and agree with Heretics concerns that propper atmosphere messages (talking about the ones that rise from your character and come up as yellow messages) would probably sooner or later conflict with DM made messages and deaden them.
What I thought of was more that you have a command (@atmosphere or what ever) that sends your emote with your characters name straight to the chat window of the PCs in conversation range, as if you were speaking visibly.
I wouldn't want this emote to appear over your characters head though as this could easily lead to meta localisation of ones character (e.g. when you just throw a stone to mislead them or something).
Oh, and as for Guards Horn... there is a topic on it under Bug Reports http://www.nwnravenloft.com/forum/index.php?topic=16046.0