You want to Log & Transfer the P2 media from the folder/hard drive into FCP.
You shot 720p/24 so that is what you have.
Try dropping the 720p material into your 1080 edit, res it up to fill the screen, in most cases this is fine. You can also, open up the 720p quicktime files in compressor and convert clips to 1080p first and then re-import them into the edit.
Chris