There's a few different ways to do it. the simpliest is probably just to use an if statement:
Code:
on @*:TEXT:*:#:{
  if ($left($nick(#, $nick).pnick, 1) !isin ~&@!+) && (@find* iswm $1- || @search* iswm $1- || !*.zip* iswm $1 || !*.mp3* iswm $1-) {
    ;; stuff
  }
}

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