May writes, “I have made a slideshow on Windows Movie Maker. I am trying to add music to it but every file I try to import says it’s not supported so it can’t be used. I am trying to use Windows Media Player files. I need them to finish this. How do I make them compatible or where do I find music compatible with the Movie Maker?”
Windows Movie Maker supports a number of file formats. Uncompressed WAV and AIFF (.aiff, .aif, .aifc) files are supported. Windows Media Audio .wma files and Microsoft’s ASF format both work with Windows Movie Maker. MP3 files can be used in movie projects. Even the slightly more obscure .snd, .au, .mpa, and .mp2 audio files should all import into the Windows Movie Maker Collections without issue. Assuming the files you are trying to use are one of the formats listed above, they should work with Windows Movie Maker. Like anything else, there are a few caveats.

Windows Movie Maker will not work with any songs purchased from places like Napster, Yahoo! Music Engine, MTV URGE, MusicNow, BuyMusic or any of the numerous online stores that sell WMA files with DRM. It also doesn’t support songs purchased through Apple’s iTunes Music Store.
Depending on what you paid for when you purchased a song from an online store, you may or may not be able to burn the song to CD. For instance, the Apple tracks are fairly easy to use – simply burn the tracks to CD and then re-rip them as MP3 files that can be used anywhere. WMA files purchased from a store like MTV URGE or Napster require a little more creativity depending on which version of the service you signed up for.
I have some tracks downloaded from MTV URGE on my system. If I try to import them into Windows Movie Maker, I get this error message:

Most of the songs purchased from an online store can be liberated by re-recording the track as it plays on your sound card. You can do this quickly using SoundTaxi to convert the song to an MP3. The other option is to do the conversion in real time with freeware app Audacity by following the steps below:
After installing Audacity, open the application and choose Wave from the input source selector in the toolbar.

Queue the song you want to use in your movie in Windows Media Player.
Start recording in Audacity.

Start playing the song in Windows Media Player. Stop recording when the song finishes.
Depending on how quickly you started recording, you may need to edit a few seconds of silence from the beginning of the recording by selecting the silence and then deleting it from the audio timeline.

Save your recording and choose File > Export as WAV to save the audio for importing into Windows Movie Maker.
Back in Windows Movie Maker, import the song you just created by either choosing File > Import Into Collections (Ctrl+I) or by dragging and dropping the WAV file into the Collections interface.

The track should now be available for use in the Windows Movie Maker Collections.