You state " Full Screen playback ".
I presume from this you are talking about playing the edited video on your PC monitor, rather than your TV ?
Have you tried altering the resolution on your monitor ?
Also its quite possible your processor's not up to the job of showing the footage full screen on your PC..( If its sub 650 mhz then it may not be able to do so, if its a higher spec ie 1Ghz or higher processor then you should be fine. )
Have you tried puting the edited version onto a DV tape then playing it through your TV.?
I presume that you Camera is Firewire in / out compatible ?