if you just wanted to output the number of days between the two dates then you should use something like this
remember: variable with quotes around it acts as as string, and therefore not a number, which is probably why your script returned 0
<?
$a = date(2003-11-26);
$b = date(2003-11-25);
$Sum = $b-$a;
echo $Sum;
?>
this should return 1 it did on my com