if (!$_GET['act']) { <form><select name="div"></select></form> }
else {
if ($_GET['s'] == '1') { //Step 1
$div = $_POST['div'];
// This part of the script pulls what option the person selected inside of the 'div' dropdown box. Then it prints a dropdown of all the usernames that belong to that 'div'. This part works.
}
if ($_GET['s'] == '2') { //Step 2
$username = $_POST['username'];
//This part selects the username then pulls a list of ranks to promote the person to and puts them in a dropdown box. Herein lies the error.
} 

$div = false;
if( isset($_POST['div']) && $_POST['div'] )
  $div = _some_data_screening_function( $_POST['div'] );

// the IFs
if ($_GET['s'] == 1) { //Step 1

}
if ($_GET['s'] == 2) { //Step 2  

}