play filename; plays a sound file or whatever can be played - This will start any file that windows media player can read.
if (playerenters){ 
  play djshadow.mp3; 
}
Plays the mp3, djshadow.mp3 when the player enters the level.
play2 filename,x,y,volume; plays a sound/music at x,y with the specified volume (1=default volume) - This allows you to specify WHERE the sound you are playing is comming from (for special effects and what not).
if (playerenters){ 
  play2 explosion.wav,1,1,.5
  setplayerprop #c,What was that?!; 
}
When the player enters the level an explosion (although it is really only the noise, not an explosion) will occur at 1,1 with a volume of .5 (can only be 0 to 1). 
playlooped filename; plays a sound file (*.wav) looped - This will play the specified wav file endlessly.
if (created){ 
  playlooped sword.wav
}
Plays the wav file "sword.wav" in a loop when the NPC is created.
stopsound filename;  stops playing a sound file (*.wav) - This ends the endless loop of a wav.
if (washit){ 
  stopsound sword.wav
}
Ends the loop of the file "sword.wav".
stopmidi; stops playing the currently running midi file - If a midi is currently looping, this will stop it.
if (playerenters){ 
  stopmidi; 
}
When the player enters the level, the currently playing midi will be stopped.
setmusicvolume left,right; adjust speaker volume - Sets the volume of the music for each speaker independently.
if (playerenters) { 
  setmusicvolume .1,1
}
This will make the music comming out of the right speaker a lot louder.  You can use something like this if for example there is a juke box on the right side of the room and you want more sound comming from that direction.
openurl URL; opens the given URL in the default web browser (without the leading http://!) - Displays a web page.
if (playertouchsme){ 
  openurl www.graalonline.com; 
}
Will displayer GraalOnline's home page when the NPC is touched.
openurl2 URL,width,height; opens an url in a window - This opens the URL faster than "openurl" and you can specify the window size.  Don't put an "http://" at the beginning of the URL.
if (playertouchsme){ 
  openurl2 www.yahoo.com,480,640
}
Will open Yahoo!'s homepage in a window that is 480x640 pixels large.
showfile filename; opens the file with the program associated with the file extension - Opens the specified file using the program that is associated with the file extension.
if (playertouchsme){ 
  showfile me2.jpg; 
}
Will show the file me2.jpg, using the program associated with .jpg.