swisscheese:The content pipeline is the only thing that will not work. It's the same story when GSE 1.0 only worked on express versions and not 2005. You can create an empty dll project in 2k5 which is used only for content processing and do the rest in 2k8 (it's a regular project with refrences). You can also move the templates around to get the wizard to work as well.
XNA Game Studio is a set of tools to facilitate programming against the XNA Framework. You cannot use XNA Game Studio 2.0 in VS 2008, because it doesn't install into VS 2008, and parts of it are incompatible with VS 2008. You can reference the XNA Framework assemblies from any managed project, in or any development environment (not just Visual Studio), but that isn't using XNA Game Studio -- it's just programming against the XNA Framework without XNA Game Studio!
Any development environment (including an "environment" made up of notepad.exe and csc.exe) can build managed assemblies that reference the XNA Framework. Not every development environment can host the Content Pipeline, provide an integrated way to configure the content builds, provide the ability to deploy and debug assemblies on an Xbox 360, support cross-platform development, or provide integrated help.
XNA Game Studio 3.0 will support VS 2008. The real path to using XNA Game Studio in VS 2008 begins with version 3.0. :-)