A request: Who has video making tips?

The other day I decided to try my hand at making a progressive-themed video for you tube.

I downloaded windows movie-maker, looked it over and began to experiment.

The first snag I hit was with importing a sound track. When I got the option to browse and select the audio file, and did that, the message I received was that the mp3 file was not valid, or corrupt.

It was an MP3 of something I recorded myself and there should be no glitches with embedded copyright tags ( whatever they are) or anything like that. I tried importing other audio files and got the same result.  

So I have a few questions for over the page;

Questions;

Does anyone know what that particular difficulty is about?

Are there other tips that anyone cares to offer about making videos that way?

How does one capture, say a portion of the video from the 'yes we can' video to use in ones own?

People seem to use any news or video footage that they like - are there not copyright concerns?

If I want stills or footage of famous people  RFK ML, JFK, Al Gore, DiCapprio, whoever, can I find those royalty free somewhere?

Are there truly free sites offering footage on a wide variety of themes?

Etc.

Thanks to anyone who can offer information on this.