Well, as a basic one, you can use Windows Movie maker, or there's a Open Source Program called Virtul Dub thats well used and recommended, but can be quite technical if you have not used an editing program before.
there's a list of some here, you can have a look see which one takes your fancy. click here
Miros, I believe David4637 is advising against the use of Windows Movie Maker if planning to export the finished videos to DVD as it doesn't convert to the neccessary file format. I'd also advise against the use of it as it is, in technical terms "a bit pants" :)