SSRS Report dependencies
I don't have 2008 to look at but do you have access to the RDL files that were published to the server?  I can't recall if those are plain old XML files, but I think if you have those, it's probably a convenient way - you could parse them with Linq to XML, or XSLT.  

The schema is documented at:

http://msdn.microsoft.com/library/dd297486%28SQL.100%29.aspx