hi, it is really easy to do that.
windows movie maker accepts wmv format so just convert your video to wmv format.
here i recommend you a really powerful video converter.
it can convert your videos to WMV/MP4/MKV/AVI and other popular formats such as: H.264/MPEG-4 AVC, FLV, MPEG-1, MPEG-2, 3GP, 3GPP, DivX, Mov, M4V, DivX, XviD, ASF, SWF, VOB, DV, Super VCD(NTSC, PAL, SECAM), VCD(NTSC, PAL, SECAM) , DVD(NTSC, PAL, SECAM) and HD video etc with high speed and excellent sound/image quality. In addition, the Total Video Converter can also extract audio from video file and convert them to AAC, AC3, AIFF, AMR, AU, FLAC, MP3, M4V, MP2, OGG, WAV, WMA as you want.
Free download it here:
http://www.aiseesoft.com/total-video-converter.html
Just have a try and i hope it will be helpful to you.