title: How to get the first day of a given week number in PHP (multi-platform)?
body: <p>What is the simplest way to do it in PHP ?</p>
  
  <p>I want the date of the Monday of a given week number of a year (example : week number 3 of 2009)</p>
  
  <p>Thanks !</p>
  
  <p>EDIT : If you use Linux only machines, use cletus' solution, however I am looking for something that can work on Windows AND Linux. </p>