do you have windows movie maker on your PC? if so, you can overdub the audio or insert video easily enough.
You can do bugger all with Movie Maker.
You can also get a free trial of After Effects:
http://www.adobe.com/cfusion/tdrc/index.cfm?product=after_effects
Again though, unsure of restrictions, but when I was using the trial of Photoshop CS6 there weren't any, so it may be the same story here.