function checkform ( form )
{
  if (form.xfirstname.value == "") {
    alert( "Please enter your first name." );
    form.xfirstname.focus();
    return false ;
  }
  if (form.xsurname.value == "") {
    alert( "Please enter your surname." );
    form.xsurname.focus();
    return false ;
  }
  if (form.xemail.value == "") {
    alert( "Please enter your email address." );
    form.xemail.focus();
    return false ;
  }
  if (form.xmessage.value == "") {
    alert( "Please enter your message." );
    form.xmessage.focus();
    return false ;
  }
  return true ;
}