I have two problems:

I cannot add an mp3 file into movie maker - it keeps saying it does not support the file type even though I have successfully managed to use the same file in another movie I made in windows movie maker.

Secondly I want to take the sound out of some clips I am editing together as there was annoying background noise and put music instead.  But I want to leave the sound in other clips as it is a voice over. How can I do this in movie maker?