SQL Server Reporting Services 2005 allows you to connect with a web based ReportViewer control.

This control needs to provide credentials for the reporting server to authenticate the user requesting the report.  By default, the account running the asp.net worker process is used, but you can use the code in this forum posting to create you own custom credentials.

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=409854&SiteID=1