function checkZipCode(area) {
  if (document.getElementById('zipCode').value.length == 0) {
    alert ('Please enter your zip code');
    document.getElementById('zipCode').focus();
    return false;
  }
  if (document.getElementById('zipCode').value.length < 5) {
    alert ('Please enter the first 5 digits of your zip code');
    document.getElementById('zipCode').focus();
     return false;
  }
  if (isNaN(document.getElementById('zipCode').value)) {
     alert ('Zip code must be numbers only');
    document.getElementById('zipCode').focus();
     return false;
  }
  
  if (area == "main") {
    var w = window.open('getlistings.php?zipCode=' + document.getElementById('zipCode').value,'Popup_Window','toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=yes, resizable=yes, copyhistory=yes, width=525, height=600');
    return false;    
  }
  else 
     return true;
}