Ajax Php Mssql ~ One drop down menu populate another! Help.

i want to populate the "component drop down menu" from the "project drop down menu".. but i don't know how to write the AJAX code for it?
can anyone help?

my goal is to find out values for $selectedProject and $selectedComponent

Thanks a lot

   <form name="myform" class="config" id="config" action="" method="POST">
   <b>Configure DevTrack Module:</b><br />

      Project:<select name="project">
      <?php
         $devtrackDB = new DBControllerDevTrack();

         $res = $devtrackDB->quick_query("SELECT ProjectName from Project");

         echo '<option value="">Select a Project</option>';

         while($data = mssql_fetch_assoc($res))
         {
            $projectName = $data['ProjectName'];

            echo '<option value="'.$projectName.'">'.$projectName.'</option>';
         }
         $selectedProject = "how to get this value?";
      ?>
      </select><br />

      Component:<select name="components">
      <?php
         $res = $devtrackDB->quick_query("SELECT ProjectID from Project WHERE ProjectName='".$selectedProject."'");

         $id = mssql_fetch_assoc($res);

         $res2 = $devtrackDB->quick_query("SELECT BugTypeName from BugTypes WHERE ProjectID='".$id['ProjectID']."'");

         echo '<option value="">Select a Component</option>';

         while($data = mssql_fetch_assoc($res2))
         {
            $bugTypeName = $data['BugTypeName'];

            echo '<option value="'.$bugTypeName.'">'.$bugTypeName.'</option>';
         }
         $selectedComponent = "how to get this value?";
      ?>
      </select><br />

      <input type="submit" value="Submit" />
      <input type="reset" value="Reset" />
   </form>

Code (markup):