Editing youtube video

I have a short youtube video located at: <[login to view URL]> I would like to add one or two slides in the beginning of the video. The slide would be similar to the one which is dispalyed at the end. Besides that I like to see if it is possible to add voice to this video. I can make a mp3 voice and would like to see if you can add it. Of course final video will replace the existing one in youtube. You need to show me somehow like adding a text in the beginning of the video so that I know you can do this. Adding sample sound is a plus. If this goes well I have more videos with the same type of editing.