Target disk mode and networking are two different things, as Target disk mode requires a restart then shutdown of one of the workstations. I've never used Firewire to network, however ,I would think it would be straight forward as the Mac should detect the ports automatically. If not you can create a new port under network status/network port configuration. Another sugestion would be to use a cat 5 lead.
This is not very hard.
Make sure both machines have firewire networking turned on - make sure that they both get IP addresses assigned by DHCP.
1) Go to System Preferences - Networking and select the Nework Status pulldown.
2) If Firewire is not on the list, press configure select the network port config on the pulldown and tick Firewire.
Both machines are now set up to use the Firewire port as a network connection.
On one machine (the Mac Pro) - go to the sharing tab and share your internet connection (Ethernet or Airport) with computers connecting via Firewire.
That's it. You are good to go.
When you plug in the MBP the Mac Pro will act as a DHCP server and assign an IP address to the MBP.
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Networking my MacBook with my Mac Pro - Firewire
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