Use the mktime function to create a timestamp for tomorrow. To go one day in the future we simply add one to the day
mktime(hour, minute, second, month, day, year, daylight savings time)
<?
$tomorrow = mktime(0, 0, 0, date("m"), date("d")+1, date("y"));
echo "Tomorrow is ".date("m/d/y", $tomorrow);
//out now date 03/03/11 tomorow is 03/04/11
?>