I've rebuilt it and tested it in Windows XP and Windows 2000. There should be no problems now.

The problem was - precisely to avoid statically linking against the C runtime and having to distribute the visual studio runtime - I had linked the program against msvcrt.dll, which is present in all versions of windows. However, the vista version of the file has more functions exported than the ones from XP and 2000. You can add a small object file that contains the missing functions as a dependency (there's a version of such object that only supplies the functions missing in XP, in w2k and w2k3), which I did, but I also had to change the crt headers folder, which I forgot to do. Oddly, in the end _wfopen_s was still missing, so I replaced it with _wfopen.