Whether you manage to find a safe backup of the original CDs or you opt for the GOG version, here is how to ensure you are playing the Pelna Wersja PL (Full Polish Version).
Here is the secret that veterans use. is a free, fan-made expansion that is now considered the definitive way to play Heroes 3. It is 100% legal provided you own the base game files. However, the developers allow a free download of a "light" version that includes the main campaign. Heroes 3 Download Free Pelna Wersja Pl