Jeg tror du kan bruge denne funktion:
<?
function DatesBetween($startDate, $endDate){
   // get the number of days between the two given dates.
   $days = (strtotime($endDate) - strtotime($startDate)) / 86400 + 1;
   $startMonth = date("m", strtotime($startDate));
   $startDay = date("d", strtotime($startDate));
   $startYear = date("Y", strtotime($startDate));   
   $dates;//the array of dates to be passed back
   for($i=0; $i<$days; $i++){
       $dates[$i] = date("n/j/Y", mktime(0, 0, 0, $startMonth , ($startDay+$i), $startYear));
   }
   return $dates;   
}
?>
Fundet på: 
http://www.php.net/date -> mybenchmarkid at yahoo dot com : 13-Feb-2007 10:55