windows authentication problem

Hi pals,
    I want to get the windows logon user. I am getting the user.
I have Default.aspx at the root level and Admin folder.
Default.aspx will have access to everybody and Admin folder only accessible to specific users.
My web.config is as below
<System.Web>
<authentication mode="windows">
</authentication>
<authorization>
<allow users="*"/>

</authorization>
<identity impersonate="true"/>

</System.Web>
<location path="~/Admin">
<System.Web>
<authentication mode="windows">
</authentication>
<authorization>
<allow users="domain\user1, domain\user2"/>
<deny users="?"/>

</authorization>
<identity impersonate="true"/>
</Syste ...