PhaseSpace,
AFAIK, there is no "MFC-to-something-else" wrapper or "MFC for Linux" available. Sorry to tell you, but you have to recode manually all the MFC calls (or write an wrapper yourselves). You know that MFC is owned by a company not very sympathic with Linux, do you

?
For the non-GUI MFC stuff ("CString"), you would have to recode it it to STL which is also available for Win32.
The main choices for portable GUI frameworks is either Trolltech's Qt (free on Linux, expensive on other platforms) or GTK (free, but somehow limited).
Wine is an option, but IMHO not a very satisfying one - too much of trade-in in performance.
Sorry, I would love to have better news.
HTH,
Peter