Hmmm.....I'm having this exact same issue with W2K3 and IIS6. It auto logins in when I go directly to http://intranet/desktopmodules/authenticationservices/activedirectory/WindowsSignin.aspx but it's not redirecting this address when I go to http://intranet/  Any ideas?

This is what I have for the whole <httpModules> area:

    <httpModules>
     <!--<add name="Authentication" type="DotNetNuke.HttpModules.AuthenticationModule,

DotNetNuke.HttpModules.Authentication" />
       <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions,

Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />-->
      <add name="Compression" type="DotNetNuke.HttpModules.Compression.CompressionModule,

DotNetNuke.HttpModules" />
      <add name="RequestFilter" type="DotNetNuke.HttpModules.RequestFilter.RequestFilterModule,

DotNetNuke.HttpModules" />
      <add name="UrlRewrite" type="DotNetNuke.HttpModules.UrlRewriteModule, DotNetNuke.HttpModules" />
      <add name="Exception" type="DotNetNuke.HttpModules.Exceptions.ExceptionModule, DotNetNuke.HttpModules"

/>
      <add name="UsersOnline" type="DotNetNuke.HttpModules.UsersOnline.UsersOnlineModule,

DotNetNuke.HttpModules" />
      <add name="DNNMembership" type="DotNetNuke.HttpModules.Membership.MembershipModule,

DotNetNuke.HttpModules" />
      <add name="Personalization" type="DotNetNuke.HttpModules.Personalization.PersonalizationModule,

DotNetNuke.HttpModules" />
      <add name="Authentication"

type="DotNetNuke.Authentication.ActiveDirectory.HttpModules.AuthenticationModule,

DotNetNuke.Authentication.ActiveDirectory" />
    </httpModules>

I've tried commenting and uncommenting certain parts and get this error every time:

Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.

Details: To enable the details of this specific error message to be viewable on remote machines, please create a <customErrors> tag within a "web.config" configuration file located in the root directory of the current web application. This <customErrors> tag should then have its "mode" attribute set to "Off".

<!-- Web.Config Configuration File -->

<configuration>
    <system.web>
        <customErrors mode="Off"/>
    </system.web>
</configuration>

<!-- Web.Config Configuration File -->

<configuration>
    <system.web>
        <customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
    </system.web>
</configuration>

Server Error in '/' Application.

---

Runtime Error

That area looks okay but whenever you get an error like you're seeing you just need to do what it says. Turn the customErrors to Off in your web.config.