Is everything being installed standalone on the XP workstation? Are you trying to install SSRS 2005? Is there a reason why you just wouldn't go with SSRS 2008 at this point which does not require IIS?

If you have ASP.NET properly registered with IIS and have installed SQL Server and SSRS 2005 I don't see what your problem is. Have you looked at the SSRS logs to see if there is any additional detail within them?

Have you tried to access the report manager or report server URL at all (http://[servername]/reports and http://[servername]/reportserver)?