Evolution uses bonobo to embed each of it's main components, I believe, so you should be able to embed it into any (Linux) program (someone may have ported bonobo to win32, I have no idea). But why would you want to? Evolution has no bloat like Mozilla does with it's XUL interface crap. It's just a large program with a lot of functionality, and isn't even in a stable beta phase yet.
(I love evolution, by the way)
About the only change you could make would be to remove bonobo, etc., even make it native win32, but why? Just use Outlook...
In the meantime, I eagerly await Evolution 1.0, it will be amazing.
Ryan