If all you need to do to make this work is assign the Mac an IP address, then here's how to do it:
1. Go to the "System Preferences" application in the Apple Menu at the top right of the screen.
2. Click on the "Network" icon in System Preferences
3. Select "Network Port Configurations" from the drop-down list, then click on the "New..." button.
4. A window will appear. In it, select the Built-in Firewire interface and then call the new network port whatever you like.
5. In the "Show:" drop-down menu, select the interface you just created. In that window, you can change the IP address, subnet mask, DNS settings, etc.
These instructions assume you are running OS 10.3.