function validate()
      
{
 if (document.user_form.un.value == "") {
 alert("please enter your username.")
 document.user_form.un.focus()
 return false;
}
 if (document.user_form.pw.value == "") {
 alert("please enter your password.")
 document.user_form.pw.focus()
 
 return false;    
}  
 return true;      
}