I've just shot a few test clips in 1080 24P on my P2 card and imported them into FCP, and FCP automatically changes the sequence settings to 1080 30P. Why is that? I just double checked the camera and it's in 1080 24P.
Maybe use the "conform" function within the program called "Cinema Tools" if available. Just right-click on the clip from within FCP, and select "Open With Cinema Tools" and select a frame rate and click "conform." When you get back to FCP, the clips may have to be re-linked/located as they will no longer match - frame rate mismatch, etc.
I could have gotten one or more things wrong in this, but that's my recollection. Good luck. YMMV