If you go
here and download
3ivx D4 4.5.1, as well as the
aac parser, WMP will play aac/m4a files.
These two links will tell you how to get stubborn WMP to add aac/m4a files to the library. You do not have to reencode.
I have no idea if this works with Windows Moviemaker, since I don't have access to that program.