I use FCP 5.1.4 (hope to upgrade to 6.0 next month), sounds like you’re on a similar version.
If you look in the FCP browser there are several columns, and in order for FCP to work seamlessly, the following have to have the same settings:
Frame size, Vid Rate, Compressor; Pixel Aspect. (I move my columns around so they are all right next to each other.)
Since all of your footage is in 1080i/24 I suggest editing in those settings. Crop in this resolution; you should be fine.
I’ll also be curious to see how any DVDs you might make appear because I have had problems shooting 720/24pn and then making dvds. It’s a time consuming hassel to put the missing fields back in. I shooting like that and now shoot in 720/30pn. Seems to make a difference.
RH