for me it always helped to not do things that would make you sweat like crazy and stay indoors as i had to. the other thing that helped was wearing breathable costumes...or costumes that allow you to keep cool in one way or another. i never really wear the same costume twice at summer cons though...it is hard when the heat and humidity make it so it is far from to go outside unless it is night.
i'd have to pull up imovie again, being i moved to fcp awhile ago. but i thought it required .mov, .dv, or mp4 files to input to it. but give me a lil time and i could try to figure out more about it since i forgot ^^;;