// Current timestamp is assumed, so these find first and last day of THIS month
$first_day_this_month = date('m-01-Y'); // hard-coded '01' for first day
$last_day_this_month = date('m-t-Y');
// With timestamp, this gets last day of April 2010
$last_day_april_2010 = date('m-t-m', strtotime('April 21, 2010'));