function chkdvdform()
{
 if(document.dvdform.firstname.value == "")  {
   alert("First name is invalid.");
   document.dvdform.firstname.focus();
   return false;
  }
 if(document.dvdform.lastname.value == "") {
   alert("Last name is invalid.");
   document.dvdform.lastname.focus();
   return false;
  }
 if(document.dvdform.address.value == "") {
   alert("Address is invalid.");
   document.dvdform.address.focus();
   return false;
  }
 if(document.dvdform.city.value == "") {
   alert("City is invalid.");
   document.dvdform.city.focus();
   return false;
  }
   if(document.dvdform.zip.value == "") {
   alert("Zip/Postal code is invalid.");
   document.dvdform.zip.focus();
   return false;
  }
  if(document.dvdform.country.value == "") {
   alert("Country is invalid.");
   document.dvdform.country.focus();
   return false;
  }
  document.dvdform.submit1.disabled = true ;
 }