function ValidateForm(form)
{ if (form.vl.value == "")
  { form.vl.focus();
    form.vl.select();
    alert ("U dient uw voorletter(s) te vullen!");
    return false;
  }
  if (form.naam.value == "")
  { form.naam.focus();
    form.naam.select();
    alert ("U dient uw naam te vullen!");
    return false;
  }
  if (!isEmail(form.e_mail.value))
  { form.e_mail.focus();
    form.e_mail.select();
    alert ("U dient uw e-mail adres te vullen!");
    return false;
  }
  return true;
}

function isEmail(str) 
{ // are regular expressions supported?
  var supported = 0;
  if (window.RegExp) 
  { var tempStr = "a";
    var tempReg = new RegExp(tempStr);
    if (tempReg.test(tempStr)) supported = 1;
  }
  if (!supported)
    return (str.indexOf(".") > 2) && (str.indexOf("@") > 0);
  var r1 = new RegExp("(@.*@)|(\\.\\.)|(@\\.)|(^\\.)");
  var r2 = new RegExp("^.+\\@(\\[?)[a-zA-Z0-9\\-\\.]+\\.([a-zA-Z]{2,3}|[0-9]{1,3})(\\]?)$");
  return (!r1.test(str) && r2.test(str));
}