On my 32 bits centos 5.4 linux system the php function mktime() returns zero for dates from the year 2038. On a 64 bits centos 5.4 linux system mktime() works fine for dates from the year 2038.

I solved the problem on my 32 bit system by using the following customized version of mktime():

function myMkTime($year, $month, $day)
{
  $tempYear = $year;
  // these two corrections are not necessary on 64 bit systems
  $yearCorrection = $tempYear >= 2038 ? 68:0;
  $iDate = 1000*mktime(0,0,0, $month, $day, $tempYear -$yearCorrection);
  if ($tempYear>=2038) {
    $iDate += 1000*mktime(23,59,59, 12, 31, 2037);
  }
  // $iDate = 1000*mktime(0,0,0, $month, $day, $year);  // use only this line on 64 bit systems
  return $iDate;
}