JQuery validation plugin - custom validation for group of html elements

Question

I have a set of combo boxes on a HTML form which act as a Date control:

 <div id="datecheck">    
    <select id="datecheck_y" name="datecheck_y">
    <option value="2009">2009</option>
    <option value="2008">2008</option>
     <option value=""></option>
    </select>
    <select  id="datecheck_m" name="datecheck_m" >
    <option value="1">Jab</option>
    <option value="2">Feb</option>
    <option value=""></option>
    </select>
    <select  id="datecheck_d" name="datecheck_d" >    
    <option value="1">1</option>
    <option value="31">31</option>
    <option value=""></option>
    </select>
</div>

No I want to validate whether the user has left any value (year/month/day) as blank, or if the values form a valid date (example invalid date: 2009(datecheck_y),Feb(datecheck_m),31(datecheck_d)

For this I wrote two custom rules in JQuery, here is my approach:

I have two custom rules (REQUIRED_DATE, VALID_DATE):

$().ready(function() {

             $.validator.addMethod("REQUIRED_DATE", function(value, element) {
             CheckBlankDate(element);
             }, "Date cannot be left blank"); 

             $.validator.addMethod("VALID_DATE", function(value, element) {
                 return this.optional(element) || CheckDate(element);
             }, "Date should be valid");


                          $("#form1").validate({                 
                              rules: {
                              datecheck: { REQUIRED_DATE: true,VALID_DATE: true }

                              },
                              messages: {
                              datecheck:
                              {
                                 REQUIRED_DATE: "Date is required",
                                 VALID_DATE: "Date should be valid"
                              }
                              }
                          });



         });

Here are the CheckDate, CheckDateBlank JavaScript functions for reference:

function ValidateDate(y, mo, d, h, mi, s) {
             var date = new Date(y, mo - 1, d, h, mi, s, 0);
             var ny = date.getFullYear();
             var nmo = date.getMonth() + 1;
             var nd = date.getDate();
             var nh = date.getHours();
             var nmi = date.getMinutes();
             var ns = date.getSeconds();

             var flag = (ny == y && nmo == mo && nd == d && nh == h && nmi == mi && ns == s);            
             return (flag);
         }

         function CheckDate(dateElement) {           
             var y, mo, d, h, mi, s;

             y = document.getElementById(dateElement.id + '_y').value;
             mo = document.getElementById(dateElement.id + '_m').value;
             d = document.getElementById(dateElement.id + '_d').value;
             h = document.getElementById(dateElement.id + '_h').value;
             mi = document.getElementById(dateElement.id + '_min').value;   
             s = 0;

            return ValidateDate(y, mo, d, h, mi, s);

         }


         function CheckBlankDate(dateElement) {
             var y, mo, d, h, mi, s;

             y = document.getElementById(dateElement.id + '_y').value;
             mo = document.getElementById(dateElement.id + '_m').value;
             d = document.getElementById(dateElement.id + '_d').value;
             h = document.getElementById(dateElement.id + '_h').value;
             mi = document.getElementById(dateElement.id + '_min').value;
             s = 0;

             if(y=="" || mo =="" || d=="")
             {
                return false;
             }
             return true;

         }

This approach does not work, as I believe JQuery cannot find any input element with name "datecheck". Is there any other approach that we can follow?