I want to write a new templating language, and I want Visual Studio to \"support\" it. What I need to know is:
I would take a look at another language that has already done the legwork of integrating with Visual Studio. A great example is Boo. The language and Visual Studio integration are open source. So you can take a look at exactly what they had to do.
The Boo Syntax Highlighting for VS2010 includes some recommended links on its homepage, which I'll copy for easy reference: