And you want:
IIS >> Apache (mod_rewrite) >> browser

iamnothing, you are correct in the above statement. If the user is redirected to B, I want B to do all of the processing and returning of the results. A should be completely out of the picture once it has performed a redirect to B. B should, however, not be known to the user and report that it is indeed A.

It should be noted that at this point, A is already doing what it is supposed to do. If it receives a request for the page www.example.com/webapp, it redirects to B. Unless I can redirect to B from A and make sure that A doesn't change the user's browser to report that it was redirected to B, I don't need to do anything to A at this point. But I don't think that IIS has that ability, although I may be incorrect.

ALL HAIL BRAK!!!