site server membership authentication with ASP.NET

[Venkatesh Namasivayam]

Am using Site Server membership authentication at the IIS
level and then trying to access an ASP.NET application.
The issue is i am not able to get the logged in user's
identity in the ASP.NET app. The REMOTE_USER or LOGON_USER
servervariables in the .NET app always return the Windows
NT Impersonation Account ("MemProxyUser") specified in the
Membership Server Instance. I have Impersonation = "true"
and Authentication = "Windows". With "Forms" i get a blank
value. Any help/insight would be greatly appreciated.