It may not come as a shock to some, but this one took me by surprise. It took some Google-ing to find the answer, but the short of it is: it does not work.
You have to deploy SSRS 2008 reports to an instance of SSRS running on SQL Server 2008 under an IIS site configured to use an SQL 2008 database.
Sorry this post is so short. I will update this post with a pertinent link as soon as I find it in my browser history on my work desktop.
:) - Cheers.