I haven't used it since I got this new windows 7 laptop, and it's really confusing me :(

I'm trying to export this audacity file into a format suitable for windows movie maker: I've tried WMA, WMV and MP3, and every time I get a message saying that "windows movie maker doesn't accept this file type" - when I KNOW that it does (at least, it used to). I've downloaded an audio converter thing, but it doesn't give me any additional options for file conversion than audacity already gave me. 

Does anyone know what I'm doing wrong?

Is the file type actually converting or does it only appear so in name? Are you creating the acceptable file outside of WMM or are you trying to change it while importing it to the software? Check audio file compatibility for your version of WMM and maybe look for a second piece of software to convert the file, maybe it would have better luck.

Also, do you have video to place this audio on top of? Maybe you can't place audio alone.

I use Sony Vegas Pro for video and Adobe Photoshop for photos , I never use the built in windows programs because they're pretty limited in formats and basic in features.

and if you're not wanting to buy anything, you can get KDenLive (a pretty good software alternative to Sony Vegas, but is only released on Ubuntu for some reason) and get GIMP (this is actually pretty easy to use and can make even Photoshop'd pictures look cheap, if you use it right)

Try converting the sound file into a .WAV file and then import to WMM. Thats what I do. I hope it helps.