If your motherboard has a live FireWire port then you will not need an additional card (unless you intend to simultaneously have more FireWire devices connected than ports available).
Insanity is hereditary, you get it from your children
I agree with Neale. One consideration is the number of controller chips you have on either the MoBo connections, or your card.
Why is that important? Especially with Capture from a camera, it is always best to ONLY have the camera hooked to a separate controller chip. Some MoBo's and cards, might have multiple connectors, but they may all feed through a single chip. That might well preclude having any other FW device hooked to any of the other connections. Sometimes, it's tough to tell the number of IEEE-1394 chips, unless one has a good schematic of the board/card and the various chips are shown.
If one uses other FW devices, then the chip count will likely matter. While I have 4 MoBo connectors w/ 2x chips, I also have a multi-chip 4x connector card, plus a multi-chip 6x FW-1394b (FW-800) card.
The two things that you wish to avoid is daisy-chaining ANY camera, and connecting a camera to any shared chip. If I had a card already, and did not need to include it with the old computer, and had a spare slot on the MoBo, I'd install it too, but then I usually have 4-6 FW-800 externals, plus maybe 4 FW-400 externals, and still have empty chips available for my camera.