Check length of video and of audio, stretch (or shrink) audio to the same length as video.
Audacity > Select All > Effect > Change Tempo > Enter new length > Ok > Try in WMM

Of course if audio length is identical to video length, then it gets more complicated

I use my sony DSC-W35 camera on video mode, macro on, sitting right in front of my DS. Previously, I used to just record the audio there on the camera, but that resulted in pretty shitty audio quality (see pretty much any Platinum video on my YouTube channel to see what I mean). This plan was to try and change it so that I could have decent audio for once…

And I’ve done as much tweaking as Windows Movie Maker will allow. If you think I’m going messing around in Audacity’s features, think again.

If so you should be able to change the sound recording to the mic in, and as a result have it all in the one file…

Otherwise, tweak, test, tweak, test, tweak, test, tweak, test, etc.