Macs don't use sound cards out-of-the-box, although 3rd party sound cards are available. SoundBlaster makes one, although their drivers haven't been updated in quite a while. I'm not sure what the exact audio processing chip is (Macs have their sound built-in to the motherboard), but it probably varies by model, since some support audio-in, some don't, and some can do optical in/out while others can't.
As for Intel-based Macs being able to use Windows-based audio/video cards, will the cards be compatible out-of-the-box? Yes, for the most part... they won't do anything at all unless Mac drivers are written for them, and that's usually up to the company that produces the card.