If you're running Windows (XP it's installed by default) you can use Windows Movie Maker. I think in Vista and 7 you have to install it via the Windows Live package though.

I've used it and it works alright. Check out the PascalGameDev channel on youtube for an example of what I've done in the past for PGD and PGD Annual related videos... http://www.youtube.com/user/PascalGameDev