Implementing ASP.NET Impersonation

Impersonation can be implemented using one of four methods:

• Impersonate the IIS authenticated account or user
• Impersonate a specific user for all the requests of an ASP.NET application
• Impersonate the authenticating user in code
• Impersonate a specific user in code

More details give in following article :

http://support.microsoft.com/kb/306158#4