The Digital Photography School blog has an instructive tutorial on using layers for those just getting their feet wet inside Photoshop, or other high-end image editors like the open-source GIMP ...

In Photoshop, you can do this in one fell swoop by pressing Option while choosing Edit > Free Transform> Flip Vertically. In Elements, duplicate the layer and choose Image > Flip Layer Vertical.

The latest iteration of Photoshop Elements--version 9--has a layer mask button, Facebook integration, and Content-Aware Fill features, and it comes packaged with the Adobe Elements Organizer.