For those who are interested, I have successfully made Intellicad load a managed/un-managed DotNET DLL , show a modal form and return the value back. A method to return the sds_getmainhwnd() to DotNET ShowDialog(IWin32Window Owner) is

NativeWindow ^nWin = gcnew NativeWindow();
nWin->AssignHandle((IntPtr)sds_getmainhwnd());
ICTools::Atest ^myform = gcnew ICTools::Atest();
myform->ShowDialog((IWin32Window^)nWin);