you should go into your capture scratch for final cut and figure out what codec you are using in final cut after it was initially captured. or, you could do it the easy way, and in final cut, you can right click on your footage and send to>shake...
when you do this it prompts you on where you want to save the shake script as well as the placeholder. the placeholder is the quicktime file that will eventually be your file out node. when shake opens, the fileOut not is already there for you with the exact same codec used in your final cut timeline. then when you finish your final composite, just hit render>file out nodes, and it will replace your place holder, and already placed in final cut for you to use. if you sent it directly from your timeline, it will put in a new video track with it turned off and in the same position as your original footage.
hope that helps you.