newbie help on refreshing page after selection from dropdown

[helloise]

<?php echo $form['catcher_id']; //gives me the dropdown list
              $catcher_names =  explode(" ",$form['catcher_id']);          
              foreach($catcher_names as $val)
              {
                  if ($val == "zed-catcher") [color="Red"]//not doing if cos page not refreshed with newley selected value[/color]
                  {
                      echo $form['service_code']->renderLabel();
                      echo $form['service_code']->renderError();
                      echo $form['service_code'];
                  }
              }
          ?>

 

from what i know i have to refresh the page with the newley selected value and the check it...and how to go about this i need to use AJAX and or javascript 

 

i am reading up on it cos i am newbie at all of this...

 

anybody to help me start on this/point me in the right direction/ explain what needs to be done please??? i dont know where to begin

 

many thanks!