Hey there. This tutorial does indeed work for Photoshop CS5, CS6, and CC(CS7).
First open up Photoshop and create a new file.
Now, type whatever you want. It doesn't matter what color your text is, because you won't see this color after you add your image unless your image is too small!
Now open up the image you want to put inside your text. Make sure the image is bigger than the size of your text! I am going to use an MLP image.
Now copy your image and paste it onto the file with your text on it. It should look something like this:
Now to put the image inside the text. Right click on your image layer and select "Create Clicking Mask."
You're done! Your image should be inside the text. Here is my finished result:
If you have any questions, feel free to comment!