title: get unix timestamp using php
body: <p>Suppose i know that today's day is monday. 
  How do i use <code>mktime()</code> in php to get unix timestamp for last friday and the friday before that?? </p>
  
  <p><strong>suppose today's date is 17-01-2011 and its a monday. Then i want the timestamp for 14-01-2011 00:00:00 and 7-01-2011 00:00:00.</strong></p>