function validate(){
  var sErr = '';
  var oInput = null;
 
    if (document.mainform.email.value == "") {
    sErr += 'Please enter your email.\n';
    oInput = document.mainform.email;
  }
  
  if (document.mainform.name.value == "") {
    sErr += 'Please enter your name.\n';
    oInput = document.mainform.name;
  }
  
   if (document.mainform.comment.value == "") {
    sErr += 'Please enter your question or comment.\n';
    oInput = document.mainform.comment;
  }

    if (sErr.length > 0) {
        // there was at least one error, output them
        alert(sErr);
        // something needs focus, set it there
        if (oInput)	oInput.focus();
        return false;
    } else {     return true;
    }
}