I would try something like this:

Code:
on *:text:*:#:{
  if ($chan == #chan1) {
    if ($nick == billgates) {
      var %string = call me
      if (%string isin $2-) { splay song1.wav }
    }
  }
  elseif ($chan == #chan2) {
    if ($nick == mom) { 
      var %string = hello
      if (%string isin $2-) { splay song2.wav }
    }
  }
}


I tested this code, and it should work.
Just make sure that the sound that you want to play is in your sounds directory:
C:\Program Files\mIRC\Sounds\
for example.