I am having the same problem to be honest with you.
I used the SONY Z1 HDV camera and imported the file in the FCP 7 on the 1080i x 1444 spec.
Now i have finished editing and i would like to export the movie on the the same format and if possible even higher.
I went on youtube and someone had posted a clip suggesting what should you do to exported for you tube use, however i need to produce a DVD with the best quality that fcp can give and if that is not possible then the original quality which was originally feed in.
Thanks