<form id="from1" name="from1"   method="post">
      <input type='text' id='textbox1' name='textbox1'/>
      <input type='text' id='textbox2' name='textbox2' />
      <input type='submit' value='submit' id='save' name='save'/>
</form>​


    <script>
    var gobalvar=false;

    $("#from1").validate({
      rules: {
            textbox2:{required: function(){
                if($('#textbox1').val()=="")//return value based on textbox1 status
                     return true;
                else
                     return false;
               }
            }
        },
            messages: {
            textbox2:'required'
            }
    });
</script>