Yes, you can include the headers and c sources to your VC++ project. In all C++ sources and headers you should add extern "C" clause to prevent from C++ name mangling.
Code:
extern "C"
{
#include "oldc_header"
}
Alternatively, you put that clause into the old headers like
Code:
// old header
#ifndef OLD_HEADER_H
#ifdef __cplusplus
extern "C"
{
#endif
// put here the olc contents of the header
#ifdef __cplusplus
}
#endif
#endif // OLD_HEADER_H
That way the extern "C" only applies if the header was included from C++ source and the old C sources would compile as well including the header.