How can i achieve the following using php
Based on week selection(1,2,3,4) of a month
1st Week: start- 5th Jan, 2012. End-12th Jan, 2012
2nd Week: 12th Jan, 2012. End- 19th Jan, 2012.
3rd Date: 19th Jan, 2012. End- 26th Jan, 2012.
4th week: 26th Jan, 2012. End- 02 Feb, 2012.