I need a freeware program to convert MP4 to a format that will play in Windows Movie Maker?

I recently got a Flip camera and all the files are in MP4 format. I want to edit my videos in Windows Movie Maker but I need a free program that will convert MP4 to any file that will work in Windows Movie Maker. Please no free trials because I don't know how long it'll be before I get an editing program that can edit MP4s :P I want a full version, not one that will only convert 75% of the file or has a watermark or will only convert videos up to 3 minutes long. I don't care what format it's in as long as it works in Windows Movie Maker. I have XP, by the way.