Code:
on 1:JOIN:[color:red]#[/color]: { 
  if ($nick != $me) { splay C:\mirc\system\sound\notify.wav
  }
}


If you want this to trigger in all channels you are in, leave the # there, if not, if you want it to trigger in a certain channel for instance in #Help..Use this..
Code:
on 1:JOIN:[color:red]#Help[/color]: { 
  if ($nick != $me) { splay C:\mirc\system\sound\notify.wav
  }
}