Windows Authentication prompts for username/password

I am trying to deploy an application in a client network, with AD/domain controller.

My application is a simple asp.net c# application, using windows authentication.

I am using win2003.

Basically, using VS2008, create a new website, hosted on IIS6.0. Only 2 changes. 1. On IIS Directory security for the application, enabled "Integrated Security".
Note: anonymous is also enabled.

Only one change to the skeleton code generated. Add below to the page_load method of default.aspx

using System.Security.Principal;
...
protected void Page_Load(object sender, EventArgs e)
{
    WindowsIdentity id = WindowsIdentity.GetCurrent();
    Response.Write("<B>Windows Identity Check</B><br>");
    Response.Write("Name: " + id.Name + "<br>");
    Response.Write("<BR>");
    Response.Write("User.Identity: " + User.Identity.Name);
    Response.Write("<BR>");
}

Output of browsing to the page: Windows Identity Check- Name: NT AUTHORITY\NETWORK SERVICE User.Identity:

The User.Identity.Name does not output the current username.

As discussed in this article http://weblogs.asp.net/scottgu/archive/2006/07/12/Recipe_3A00_-Enabling-Windows-Authentication-within-an-Intranet-ASP.NET-Web-application.aspx

I added:

<authorization>
    <deny users="?"/>
</authorization>

From what i userstand is that, when this is added, I can get the current users, username from User.Identity.Name.

However, once I added the above, the browser now prompts me for a username and password. Once I enter it, I am able to use User.Identity.Name to get the username. However I do not want the username/password pop up to appear. I w