Re: GP 9.0 SDK for VS2008?
There is no Visual Studio 2008 version of the VS Tools SDK. There's a good chance that you'll be able to make it work with Visual Studio 2008 however. You'll need to install the samples, which are in Visual Studio 2005 format. Make a copy of the samples and then open them with VS 2008, which will upgrade them. You should be able to compile them, and verify that they work. If they do, then use those sample projects as your template for creating your own project.
There's nothing too magical about the templates that are installed for VS Tools. They just make it more convenient to create new projects, because they already contain the appropriate assembly references, resources, and some template code. The samples will also have those same things, because they were created using the templates.
Hope this helps.