Visual Studio 2008 Service Pack 1 is not finished yet, but we do have a beta version of the documentation ready for you to read! You can learn about some of the features that you'll see later this year when we release SP1.
I recommend starting with reading about a totally new feature that we put into SP1 that allows you to extend Word documents and Excel Workbooks at runtime from an Application-Level Add-in. Here is the link to the Beta of the documentation:
Microsoft, Visual Studio, SP1, Beta, Documentaion