Aside from being crap, Windows Movie Maker only handles
Video files: .asf, .avi, .wmv
• Movie files: MPEG1, .mpeg, .mpg, .m1v, .mp2
• Audio files: .wav, .snd, .au, .aif, .aifc, .aiff
• Windows Media files: .asf, .wm, .wma, .wmv
• Still images: .bmp, .jpg, .jpeg, .jpe, .jfif, .gif
• MP3 format audio: .mp3
If you want anything better you can either get a codec pack from tucows or get an alternative video editing app like Adobe Premier, Ulead Studio, Sony Vegas
Windows Movie Maker doesn't do hi Def mpeg but iMovie does.
or Get a Mac