<script src="path/to/jQuery compatible with plugin"></script>
<script>
  /* must call this before loading other version*/
  $jQ_1.8= $.noConflict();
</script>
<script src="jquery-1.3"></script>

<script>
/* use "$" as you normally do for exisitng site code*/
  $(function(){
      /* code using 1.3*/
  })

/* for higher version jQuery use different *document.ready**/
$jQ_1.8(function( $){/* pass "$" as argument to allow using "$" in code if you want*/
  $(selector).pluginThatUsesDifferentVerion()

})