Cutting up a sawtooth case is just like cutting up any other case. The only thing is you will have a layer of metal and a layer of plastic to cut though. What I would do is cut a hole in the metal that is bigger then the firewire input and make a hole in the plastic that is the same size as the firewire input and mount the firewire cable to the plastic. Or if you don;t have a ZIP drive or a hard drive in the bay under the CD/DVD drive you can just mount the firewire there and only face cutting one layer of plastic.
To live is to let die