[Oblivion Knight]

To integrate this into the control panel, I did the following:

Open admin/index.php
Find:

makenavoption("IP Addresses","user.php?action=doips","<br>");

Add AFTER it:

makenavoption("Duplicate IPs & PWs","dupeip.php?action=","<br>");

Open admin/dupeip.php
Find:

require("./global.php");

Add AFTER it:

if (isset($action)==0) {
  $action="modify";
}