A really simple and easy program to use is Window Movie Maker 2 (http://www.microsoft.com/windowsxp/moviemaker/default.asp
If you have time to learn a more complex editing program and can acquire a copy, check out Adobe Premiere 6.5 for windows or Final Cut (or Final Cut Pro) for the Mac.
Some tip on taking the video:
1) Record only the action! People often record a rider's entire session keeping the tape rolling the whole time. Fight the urge! You'll end up wasting 15 minutes of tape, only to use 2 minutes worth in your final edit.
2) Start, stop, start, stop, start, stopů. Press the record button when you see the rider start their outside cut. Now stop recording 2 -3 seconds after they land.
When it's time to compress your video check out my post on http://www.wakeworld.com/MB/Discus/messages/1/76852.html