DirectX 10 will be better for physics, but not great

DirectX 9 doesn't yet have its physics 'A' level. For example, you first have to create a 3D box and set its vertices and pixels and, even when you render it, you still cannot manipulate it on a physics level.

Once you make the 3D box, you need to use the Ageia Physx chip (or something like it) to physically design the box and only after that can you play with, move, fiddle with or break your 3D box.

DirectX 10 will automatically create the 3D box and a physics box and will make the implementation of physics much easier than before. DirectX 10 can do some incremental physics and is introducing the geometry Shader that will help mimic the real-world physics of rigid bodies.

However, DirectX 10 will still inherit some overhead problems of the old DirectX. It will very much depend how you use it and how you implement it. µ