[0] => Array
    (
        [0] => REPORTIDXXXXXXXXXXXXXXXXXXXXXXXXXXX
        [1] => REPORT EXPORT NAME#1
        [2] => REPORT DESCRIPTION #1
        [3] => 2012-10-02T17:31:30
    )

[1] => Array
    (
        [0] => REPORTIDYYYYYYYYYYYYYYYYYYYYYYYYYYYYY
        [1] => REPORTOTHERNAME#2
        [2] => REPORTDESCRIPTION #2
        [3] => 2012-09-28T15:15:17
    )

[2] => Array
    (
        [0] => REPORTIDZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
        [1] => REPORT EXPORT NAME#3
        [2] => REPORT DESCRIPTION #3
        [3] => 2012-09-28T14:59:17
    )

function get_report_ids(array $rs) {
   $results = array();
   // loop over your data structure
   foreach($rs as $key => $data) {

      // If element 1 contains EXPORT (case insensitive)
      if(stripos($data[1], 'EXPORT') !== false) {
         // regex to capture the ID from element 0
         if(preg_match('/^EXPORTID(.*)$/i', $data[0], $matches)) {
            // add the ID to the results array
            $results[] = $matches[1];
         }
      }
   }

   // if we had results then return the array, otherwise return null
   return !empty($results) ? $results : null;
}

array(
  0 => 'XXXXXXXXXXXXXXXXXXXXXXXXXXX',
  1 => 'ZZZZZZZZZZZZZZZZZZZZZZZZZZZZ'
)

$array = array(
0 => array(0 => "REPORTIDXXXXXXXXXXXXXXXXXXXXXXXXXXX",1 => "REPORT EXPORT NAME#1",2 => "REPORT DESCRIPTION #1",3 => "2012-10-02T17:31:30"),
1 => array(0 => "REPORTIDYYYYYYYYYYYYYYYYYYYYYYYYYYYYY",1 => "REPORTOTHERNAME#2",2 => "REPORTDESCRIPTION #2",3 => "2012-09-28T15:15:17"),
2 => array(0 => "REPORTIDZZZZZZZZZZZZZZZZZZZZZZZZZZZZ",1 => "REPORT EXPORT NAME#3",2 => "REPORT DESCRIPTION #3",3 => "2012-09-28T14:59:17")
);

$array = array_map(function ($var) {
    preg_match('/^REPORTID(w+)/i', $var[0], $result);
    return $result[1];
}, $array);

var_dump($array);

array
  0 => string 'XXXXXXXXXXXXXXXXXXXXXXXXXXX' (length=27)
  1 => string 'YYYYYYYYYYYYYYYYYYYYYYYYYYYYY' (length=29)
  2 => string 'ZZZZZZZZZZZZZZZZZZZZZZZZZZZZ' (length=28)