Be sure that all devices are on the same network.
If apple tv and remote are on same homeshare you should be able to select and control the apple tv from with in the remote app.
If apple tv and the itunes are on the same homeshare the apple tv will see the itunes library (and shared photos) in the computer section.
Additionally if these are all on the same homeshare you should see both the apple tv and the itunes library in the remote app.
hope that helps.