From: Daniel Piechnick
Hi Rick. The simplest way to do what you're taking about would be to create text, by using the Text Tool in Photoshop, then Ctrl+Click the text layer in the layers list, to select the shape of the text. Then click on the layer that your photo is in, and press Ctrl+C to copy whatever's inside your selected area. Create a new layer, and press Ctrl+V to paste. You can then get rid of your other layers. There are other ways to do this in Photoshop, by defining patterns and such, but that's not really necessary in this case.