Why can't I upload a video on YouTube? (Changing file formats)?

I just made a video for the first time on Windows Movie Maker (it sucks). I tried to upload it to YouTube but it said it failed because it was an invalid file format. So, how do I change the file format (that must be the problem)?Why can't I upload a video on YouTube? (Changing file formats)?Make sure your trying to upload a wmv or avi from wmm. Users have tried to upload a saved projects file mswmm, getting invalid file format.Why can't I upload a video on YouTube? (Changing file formats)?you need real.com then it will go