Here's a tip for some would-be HD shooters wondering why get a 1080i or 1080p camera - two shots for the price of one. I always edit 720p, because that's what most local TV stations are putting out right now. But, if you shoot 1080, you really get two shots in one.

Just capture your footage, bring it into a 720p timeline, and start cutting. If you need some shot variance, just right click a clip and deselect 'scale to frame size', and magically you go to a tighter shot.

This way, you can cut back in and out of the action.

As I've said before, doing a great green screen key is one of the most difficult effects you can pull off. It's amazing that so many people attempt it as their first effect, only to be frustrated at the results. Unlike broadcast, most people shoot with MiniDV or HDV, which, by default, are compressed formats. 
Not to worry, though...read on and you'll get the shot you're after.