The initial version of Time Capsule will not allow streaming directly to Apple TV. It is uncertain if this will be something that will be allowed in future versions or not.

Despite direct to device renting available, Apple TV continues to be dependent on iTunes for synchronization. If (and it’s a big if) the Time Capsule can be used as network storage, it should be theoretically possible to use it to store the iTunes library externally.

External drive (air disk) -> computer with iTunes -> Apple TV

However, most people agree that currently iTunes does not handle network shares smoothly or consistently.

The dream of dumping all the media on an external device and using it without an additional box is still a far dream away.