Using Text as a Mask
Masking is a very easy tool in Fireworks. We will take a photograph and mask it with a string of text. You can use your own image, or the one I have supplied. The photo I used is shown below and was found at http://www.espectro.com/:

Open a new Fireworks document. Set the dimensions to 600 x200 pixels and set the canvas color is set to transparent or white.
Import the image you wish to use as the "fill" for the text. Go to File > Import and browse for the image. Once you locate it, open the file in the Browse dialog box. If you're new to the Import function, the first thing you will notice is that the image does not open immediately, but the mouse cursor changes to an inverted "L" shape. If you want to size the image to fit within your canvas area, click and drag the cursor. When you let go, the image will be inserted at the desired proportional dimensions. If you want to import the image without sizing, click anywhere on the canvas.
Choose the Pointer tool, hold down the Shift key and click on the image behind the text. Both images are now selected.
Choose Modify > Mask > Group as Mask. The photo shows through the text, but is invisible anywhere else!

The great thing about masking is editability; the text is still editable and the image is still movable. If you select the text tool again and click inside your text, you will see your cursor change. You can edit the text in this way. If you want to make a lot of changes to the text, go to Text > Editor to bring up a more robust editing tool.
By using the Pointer tool, you can reposition the entire image by clicking and dragging.