Hi,
I have recently committed required changes to Mono SVN repository as r102052.
Now Mono has mixed-mode assembly support on Windows. These is no full MSVCRT support because that heavily depends on the unmanaged API of .NET Framework but programs compiled using Microsoft Visual C++ and not using MSVCRT should be supported. Even exporting functions in managed DLLs is supported that is supported by ildasm.exe and ilasm.exe as well.
When the process is created using mono.exe there are some limitations for executable assemblies but with a custom mscoree.dll Mono has full support to create processes from managed executables.
The attached mscoree.c is the source code for a custom mscoree.dll that uses Mono for creating processes from executables. I think that you should incorporate this into your mscoree.dll. Also note that you should only provide not implemented stubs in your mscoree.dll and implement missing functionality in Mono's coree.c if required.
mscoree.c and http://anonsvn.mono-project.com/viewcvs/trunk/mono/mono/metadata/coree.c contains some comments about managed module support in ntdll.dll and msvcrt.dll of XP and later. If someone volunteers this could be implemented in Wine as well.
Kornél