<?php

function RetSemana($data){

   $aVet=Explode("/",$data);
   $dat = date("d/m/Y", mktime(0,0,0,$aVet[1],'1',$aVet[2]));
   $semana = ($data-$dat)+date("w",mktime(0,0,0,$aVet[1],'1',$aVet[2]));
   $semana = substr(($semana / 7),0,1)+1;
   return $semana;
}

echo RetSemana("26/04/2006");
?>