make textbox visable on client side with javascript

Hi guys,
I'm trying to make it so a few textboxes become visable when the user clicks on a button on the client side before it goes back to the server. when the page loads the textboxes are initally invisable. What I can't seem to figure out is how to find the Textbox on the page in javascript. here's my code.

Code:

---

<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<script type="text/javascript">
    function script2() {
        alert('Hello!');
        document.getElementById('TextBox2').style.visibility = 'visible'
    }
</script>

'the button that triggers the script
        <asp:Button ID="Button1" runat="server" Text="Specify Period" OnClientClick="script2()" Width="108px" /><br /><br />

'the textbox I'm trying to find.
<asp:TextBox ID="TextBox2" runat="server" Visible="False" Width="70px">01/25/09</asp:TextBox>&nbsp;&nbsp;&nbsp;&nbsp;

---

I was looking in document innerHTML and it seems that textbox2 isn't even in there.

I tried document.getElementById('MainContent_TextBox2')
too and that didn't get anywhere.

also tried document.forms[0] but it appears by textbox isn't there.

thanks guys