$(document).ready(function() {  
  $("#search").keydown(
    function(event) {
      if (event.keyCode == 13) {
        if ((document.forms[0].search.value=="Click to Search...") || (document.forms[0].search.value=="") ) {
              alert("You must enter a search term"); return false;
        } else {
             window.location='/search?q=' + escape(document.forms[0].search.value);
        }
      }
    })
});