Filling Text with an Image

Open an image that you want to place into text
Make your Layers palette visible
Convert your background to a layer. You can do this by double clicking the Layer name and accepting the default name of Layer1. You can also do this by Alt-double clicking. Your Layers palette should look like the figure below.

Now add your text. I'll use Impact, fairly large text. This can always be changed prior to flattening the image. By the way, the text can be any color - this will be explained later on.
Drag the Text layer to the bottom. Your Layers palette should look like the figure below.

Now we're going to group the 2 layers but first a little theory. When 2 layers are grouped, we form what is called a clipping group. This means the the upper layer will show through wherever the bottom layer contains pixels, regardless of the color. In other words, the top image will only show where you placed text.
The layers can be grouped several ways. One way is to Alt-click the border between the two layers as shown below. Make sure that the upper layer is selected first. You can also group the layers by using Layers->Group with Previous.

Your image will look as shown on the left below. If you add a white-filled layer and place it on the bottom of the layer stack, your image will look as shown on the right below.

Now for the fun part. With the Text Layer selected, apply a Layer Style of your choice. The image below has a simple inner bevel applied but you can experiment here.

Before flattening your image you can select the image which is the top layer, choose the Move tool and with the arrow keys on the keyboard, move the image until the most interesting part of the image fills the text.
Now you can flatten you image. For more fun, this text can be placed into another image to make an interesting opening for a slide show. See an example below. Here we increased the canvas size to allow the text to sit outside the image.