AppleTV streaming from Airport Shared Disk?
Further to Paul's comment, if you place your iTunes library on the remote disc it will work fine, but obviously you won;t have access to it when you are on the move out of range of your home wifi.

But you can create multiple iTunes libraries, and have one on your macbook, and one on the remote disc.  Hold the alt/option key when starting iTunes to be presented options for creating/choosing an alternative library.

In order to stream from the library on the remote disc, you will need iTunes running, with the correct library selected.  You will also need Homeshare set up both in iTunes and your Apple TV.

Good luck.