Wow, I feel your pain. I bet you wish now you had spent about 10% of your 2 day research time before you actually shot the interviews. I have seen some fairly decent keying done with DV footage in FCP although I have never seen it projected to a 12×12 screen. Unfortunately, being that you have tried so many different options, all with similar results, your problem may go a lot deeper than the keying options you are trying. It may have to do with the lighting used and possibly the seperation between your subject and the green screen, in which case no matter what you try you will end up with similar results.