@Quel:
First you have to pick up the end of one of the chains and pull it in the opposite direction of where the boss is walking, to make him trip and lose his mask, piece by piece. Do this a total of three times and his mask will be completely destroyed, and he will rip of his chains in rage. :)
Step two is to reflect the energy ball he is throwing, using your shield or sword. Because his face is now unprotected, he will die after two hits.
@Gorlock:
That's weird. I don't have a machine running vista, but it shouldn't be any different from w7. Make sure all the folders have their original names and that you have directx 9 installed. Other than that I have no idea what might be causing it.