Hi Victoria,
Firstly, you will need to have your chosen images which you wish to view on your Apple TV rendered in Aperture to create a preview.
Choose a handful of your favourite images destined to the Apple TV. Place them in an album. I personally call my album for this "Apple TV Screensaver"
Then go to iTunes / File / Home Sharing / Choose Photos to Share with Apple TV...
Find the name of the album and check this.
Keep iTunes open.
Go to your Apple TV.
...Settings / General / Screensaver / Type and then select Home Sharing, from the Photos option you should see the name of your Aperture album. Be patient. Let them sync across.
I have found that I sync about a hundred or so images.
G