Applying a text mask to an image in Photoshop is not as hard as you might think as can be found in this guide. In the guide I've used Adobe Photoshop CS2, but it should work in other versions too.
A question I've been asked by a few visitors recently is how to use text as a mask, thankfully it's not that complicated a task and so is very quick and easy to understand. The first thing to do is to get your image and make sure it is not locked, or is not a background layer. For this example I've just used a picture of some water from stock.xchng.
Now the next step is to use the Text Mask tool (press T, or press and hold on the T icon in the toolbar).
You'll notice that the image turns a pinkish shade of red, but don't worry, this is so you can see where your mask will lie. Now click on the image and type your text, and when you're done use the Marquee selection tool to move it if you don't get it in the right place. Using the move tool will not work as expected.
When you've done, make sure you layer is selected, and then click the "Add Layer Mask" button at the bottom of the layers palette.
And as you can see it's all done, and wasn't that hard!