David Ebbo wrote a very interesting article that explains in great details how they gave ASP.NET the ability to be driven by dynamic languages. The compilation system, on which David worked for a few years, is explained, as well as why it doesn't apply to dynamic languages. Then he goes on to explain how they were able to integrate IronPython anyway, taking advantage of an existing feature, no-compile pages.
One of the surprising things is that dynamic languages will actually perform better for a whole class of applications.
Check it out: http://www.asp.net/ironpython/WhitePaper.aspx?tabid=62