I created a report and published it to the Report Server 2008 that worked fine. I can call http://servername:81/Reports in my browser and view and expo
Maybe you haven't specified the .asmx (web service) address...
This MSDN article is from the SQL Server 2008 Books Online which should be useful. Also note the "Other Resources" link to Building Application using the Web Service...
Just checking the config file for one of our applications that uses the web service and the address stored is:
http://SERVER_NAME/ReportServer/ReportService.asmx
so yours might be:
http://SERVER_NAME:81/ReportServer/ReportService.asmx