I want to write a new templating language, and I want Visual Studio to \"support\" it. What I need to know is:
Regarding the Visual Studio aspects, what you need is a "language service", which is the entity that handles colorizing, intellisense, etc. for a given file extension/type.
For an intro, see this article
And for a code sample see here
Regarding parsing, there are lots of technologies, and I won't offer an opinion/advice.
Beware, there is a fair amount of work involved, although in my opinion it is much more straightforward in VS2010 than in previous versions of Visual Studio to provide this kind of extension.
See also
Visual Studio 2010 Extensibility, MPF and language services