You need to make sure that your printer is properly installed on your Mac OS. As you can see in the image below, this printer doesn't have support for Mac OS 10.5.5. This is the main reason OSX doesn't recognize the printer.
You will have to contact Brother in order to obtain a driver for your device. Use the following URL: http://www.brother-usa.com/askus/
Note: The serial number is on the white sticker attached to device.