<?
$first_date = mktime(12,0,0,1,1,2005);
$second_date = time();
$offset = $second_date-$first_date;
$this_day = floor($offset/60/60/24);
?>
<? if ($this_day % 2 == 0) { ?>
<!-- spit something -->
<? }else{ ?>
<!-- spit something -->
<? } ?>