select floor((last_day(trunc(dte)) - trunc(dte,'MM'))/7) --  1 per complete week
      ,case when to_char(trunc(dte,'MM'),'D') + mod(last_day(trunc(dte)) - trunc(dte,'MM'),7) >= 7 then 1
            else 0 
            end
from (select to_date('07-07-2006','dd-mm-yyyy') dte from dual);

select sum(decode(to_char(dte,'D'),7,1,0))
from  (select trunc(to_date('07-10-2006','dd-mm-yyyy'),'MM')+level -1 dte
       from   dual
       connect by level <= to_char(last_day(to_date('07-10-2006','dd-mm-yyyy')),'dd'));

SQL> select count(thedate) x
  2  from   ( select to_date('200605','YYYYMM')+level-1 thedate
  3           from   dual
  4           connect by level <   add_months(to_date('200605','YYYYMM'),1)
  5                              - to_date('200605','YYYYMM')
  6         )
  7  where  to_char(thedate,'DY','NLS_DATE_LANGUAGE=AMERICAN') = 'SUN'
  8  /

         X
----------
         4

select to_char(sysdate,'FMMONTH YYYY') MONTH,
	ceil(to_char(trunc(last_day(sysdate)+1,'IW')-1,'DD')/7) SUNDAYS from dual;

MONTH	     SUNDAYS
------------ -------
OCTOBER 2006       5