You cannot capture any native modes through firewire (no 720p24pn). You can however capture 720p24 and FCP will remove duplicate frames.
Go to your Fincal Cut Pro > Audio/Video Settings and select your sequence and capture settings to DVCProHD 720p24.
Open your log and capture window, set the external device on the right to Uncontrollable Device.
If your camera is connected to the firewire port and it's turned on, you should see the preview window in FCP displaying the cameras view. If this is the case, you are ready to hit the Capture Now button. If you see bars in FCP and blue in the camera's lcd, you are in Firewire communication mode (the same one you use to ingest from P2) which is wrong for live capture and you need to turn the camera off and back on again.
