I've found a solution to this problem, so I wanted everyone to find it. In the older Windows programs, you can choose which program opens in editing, but in Windows 7 that feature is disabled. If you download the following program, click File Type Settings > Context Menu > then, for example "PNG" extension-- you can choose which program OPENS a PNG, which program EDITS a PNG, etc. That way you can view a photo in Windows Photo Viewer, but edit in Photoshop. Brilliant!