To access your Aperture library:
Choose File > Show Aperture Library.
The same view of your Aperture library organization that you see in Aperture appears on the left side of the window.
To move photos from your Aperture library to your iPhoto library, select the photos in your Aperture library and drag them into iPhoto.
A duplicate of the photo or photos now exists in both applications, but theyre completely separate. If you edit the photo in iPhoto, those edits do not affect the copy in your Aperture library, and vice versa.
If you dont see your Aperture library, open Aperture, choose Aperture Preferences, and make sure youve selected the checkbox to Share previews with iLife and iWork.