Add a msgbox if condition is true

When the user clicks the submit button, I run a function that validates the fields. The page will not submit unless the conditions are met. I want to know how to add a msg box if all the conditions are met....

<form id=Frm name=Frm method="POST" action="Page2.asp" onsubmit="Valid()">


<script language="Javascript">
function Valid()
{
if (Frm.txtName.value == "")
{
alert("Enter Name!");
Frm.txtName.focus();
event.returnValue = false
}
}

What do you mean by a message box, at first I thought you meant an alert(), but I see you know how to use them.

just FYI, I would only alert the user if something is wrong. If everything is ok, the page should just submit to a thank you page or something similar. (This would be more easily implemented in PHP, mind you.)