HTML код:

<script language="javascript" type="text/javascript">
function submitbutton_reg() {
var form = document.regForm;
if (form.name.value == "Ф.И.О.") {
	alert( "Введите корректные данные!" );
} else {
form.submit();
}
}
</script>
<form action="register.php" method="post" name="regForm">
<input id="cname" name="name" type="text" value="Ф.И.О." onfocus="this.value=(this.value=='Ф.И.О.'?'':this.value)"  onblur="if (!this.value) this.value = 'Ф.И.О.'" size="25" class="required" minlength="2">
<input type="button" value="Отправить" class="button" onclick="submitbutton_reg()" />
</form>