Code:
; only add requests that aren't in there yet
on *:TEXT:.request*:?:{
  if ($read(requests.txt, w, $2-) == $null) {
    /write -i requests.txt $2
  }
  else { msg $nick That has already been requested. }
}

; delete requests
on *:TEXT:!delrequest *:?:{
  if ($read(requests.txt, w, $2-) != $null) {
    var %blah = $read(requests.txt, w, $2-)
    .write -d $+ $readn requests.txt
  }
  else { msg $nick There is no request on file for $2- }
}


haven't tested it, just came up with it in my head, but it should work.

-Venoman