I have an Intel Core Duo processor, and like some of you, I had serious audio/video sync problems. After a lot of looking around, I found this Microsoft Support Article:
I installed the hotfix mentioned there, and all my synching issues are fixed. The game runs absolutely perfectly now.
If you have a multi-core processor, and just cannot seem to get this problem solved, give this hotfix a try. It's not public yet, so you'll have to give Microsoft a call to get the hotfix for free. (Or google for it, but uh, you didn't hear that from me.)
NOTE: This solution is only for people with a multi-core processor!
For AMD dual-core users, there is a official AMD fix at [URL=http://www.amd.com/us-en/assets/content_type/utilities/AMD_Dual-Core_Optimizer_113.zip]. It solved the problem for me instantly. All the other solutions failed. I hope it helps others too.