<asp:PlaceHolder ID="AdminModHolder" runat="server" Visible="false">
              <ul class="menuAdminList">
                 <li class="menuAdmin"><a title="Go to Ads Manager" href="http://localhost:20937/adsmanager.aspx" target="_top">Ads Manager</a></li>
                <asp:PlaceHolder ID="menuAdminItems" runat="server"></asp:PlaceHolder>
              </ul>
            </asp:PlaceHolder>

<if url="^((?!\.ashx|\.asmx|\.axd|\.gif|\.png|\.jpg|\.ico|\.pdf|\.css|\.js|\/install|error\.aspx|auth\.aspx|default\.aspx|popup\.aspx|advanced\.aspx|digest\.aspx|ftb.imagegallery\.aspx|ckfinder).)*$">
    <rewrite url="^~/(.+)?\?(.+)?$" to="~/Default.aspx?g=$1&amp;$2" processing="stop" />
    <rewrite url="^~/(.+)?\.aspx$" to="~/Default.aspx?g=$1" processing="stop" /> 
    <rewrite url="^~/(.+)?$" to="~/Default.aspx?g=$1" processing="stop" />
  </if>

<if url="^((?!\.ashx|\.asmx|\.axd|\.gif|\.png|\.jpg|\.ico|\.pdf|\.css|\.js|\/install|error\.aspx|auth\.aspx|default\.aspx|popup\.aspx|advanced\.aspx|digest\.aspx|ftb.imagegallery\.aspx|ckfinder|adsmanager\.aspx).)*$">
    <rewrite url="^~/(.+)?\?(.+)?$" to="~/Default.aspx?g=$1&amp;$2" processing="stop" />
    <rewrite url="^~/(.+)?\.aspx$" to="~/Default.aspx?g=$1" processing="stop" /> 
    <rewrite url="^~/(.+)?$" to="~/Default.aspx?g=$1" processing="stop" />
  </if>

if (HttpContext.Current.User.Identity.IsAuthenticated)
                    {
                       // do action if user is logged in
                    }
else  {

// do other action if user is aguest
}