Reporting Services 2008

Execution Account (Reporting Services Configuration)

http://msdn.microsoft.com/en-us/library/ms181156(v=SQL.100).aspx

How to: Configure Custom or Forms Authentication in Reporting Services

http://msdn.microsoft.com/en-us/library/cc281383%28v=SQL.100%29.aspx

Enabling Report Manager to Pass Custom Authentication Cookies

http://msdn.microsoft.com/en-us/library/ms345241%28v=SQL.100%29.aspx