Jeanne,
when you open an image in Adobe Photoshop, then by default the edited version will be saved in the same folder as the imported original image. You can select a different location when you are saving (as) or exporting the image in th file choser dialogue.
The easiest way to quickly find your saved image would be to launch Photoshop again and to use the main menu bar:
File > Open recent
Your recently saved image should appear at the top of the list of recent imaged.
If you cannot find it there, search for it with Spotlight, if you remember a part of the filename.
How did you open the image in question in the first place? If you used Photoshop as external editor, then Photoshop will probably have stored the edited PSD-file inside the Aperture Library Package, and you will not see it in the Finder, but Aperture will. It may look funny, however, in Aperture, for Aperture cannot display the layers.
Regards
Léonie