Assuming that you have FCE HD (and Quicktime Pro), you have a couple of options:
1) you could capture at 720x1280 at 30fps encoding with Apple Intermediate Codec (AIC). That is HDV 720p30, which FCE recognises. You might have to load it into QT Pro and export it again to make sure the frame rate is right - I've read about some issues with that. Hopefully that will be big enough to see what is going on for most applications you might capture.
2) you could capture at full screen resolution, and then export from QT Pro as HD 1080i50 or 1080i60 before editing. That will be much more demanding to edit on your system than 720p, but you will get the full screen resolution to play with.
Hope that helps (and is not too late!)