Here's a simple one..

Code:
alias mp3 {
  set %mp3dir $$sdir=" Set Mp3 Directory: "
  write -c mp3.txt
  noop $findfile(%mp3dir,*.mp3,0,write mp3.txt $1-)
}

on $*:text:/!(play|stop|pause|resume|random)/Si:*:{
  if ($isfile(mp3.txt)) {
    if ($1 == !random) splay $read(mp3.txt,$r(1,$lines(mp3.txt)))
    if ($1 == !play) splay $read(mp3.txt,$2)
    if ($1 == !stop) splay stop
    if ($1 == !pause) splay pause
    if ($1 == !resume) splay resume
  }
}


Simple put this in your bot, type /mp3 to set your directory. And in your mIRC/Script type the above commands.

!play 5 - Plays the fifth mp3 in your mp3 file, etc. It's just a pretty basic one as I have to go out now, I'm sure you'll get more responsive replies soon.