Hey man...I hope this answer will help you out...
You could do it inside the game while watching the replay I think it's called extract or something but that takes forever...
What you need is called Fraps. I think you can get a trial version at
www.fraps.com and this will allow you to record your game and it will save it as an AVI file which you can import into Windows Movie Maker for editing...but the only downside is that Fraps makes the .AVI files really big because it's making them live as you record...but after you save your file in Movie Maker it should shrink it down some, or you could download an AVI compressor somewhere online, also.