Does anyone know about COFF debuggers?

I'm building an MFC 6 user interface onto a BIG application which contains a lot of Legacy code written in ADA, C and FORTRAN ( probably 100 man years effort into this code, at least).

All this code is contained within DLL's, the FORTRAN is not a problem because the compiler is an old MS one and can generate PDB debug. The ADA is the bit I'm interested in because thats where I'm having to hook into from MFC, this is compiled using Gnat ADA 3.04a which cannot generate PDB debug info, but it can generate COFF info. Does anyone know of a debugger which runs under NT and will debug COFF (preferably on a time restricted licence so I can try it out), the MSDEV environment says it can generate COFF aswell but it doesn't seem to want to play ball when it comes to debugging and the help doesn't offer much. I downloaded a debugger from Gnat which is a port from Unix but that doesn't seem to work properly.

Any help would be appreciated very much...