in the date function
(http://www.php.net/manual/en/function.date.php)

Example 3. date() and mktime() example 
$lastmonth = mktime (0,0,0,date("m")-1,date("d"),date("Y"));

i use it in the 31.4

like this:
$month= mktime (0,0,0,date("m")-2,date("d"),date("Y"));
i got "march";
because february only have 28 days .

i use:
$month= mktime (0,0,0,date("m")-2,1,date("Y"));
instead;

noam