Windows Movie Maker, a multimedia application bundled with Windows Vista, Windows XP and Windows Me, supports a variety of video and audio formats. Windows Movie Maker doesn't include native support for these formats out of the box, but it can download codec updates allowing the program to open and save additional formats. Windows Movie Maker can install the required codecs automatically when you open a video file that requires them, although this feature is disabled by default.
Click the "Tools" menu at the top of the Windows Movie Maker window and select "Options."
Click the "General" tab at the top of the Options window.
Enable the "Download Codecs Automatically" check box on the General pane by clicking this option.
Click the "OK" button.
Click the "File" menu and then click "Import Into Collections." Browse to a video or audio file on your computer that requires a new codec and double-click the file to open it. Windows Movie Maker will automatically download the required codec updates from the Web.