If u would like to make a small Videoclip and use the technology of blue boxing or also called chroma effect (you know that stuff when superman flies in the clouds or behind the new speaker in television the pictures come blended in). You can use Movie Maker in Windows and some help from the guys of http://www.windowsmoviemakers.net/ There are several tutorials how to do ith windows movie maker 2.0 (thats in xp also free to download in the net) and as I did with Movie Maker 6.0 in Vista. For the last, you download the ShaderFx from http://www.rehanfx.org/shader.htm and just install it (its shareware).
Than you import your video that you did infront of a blue wall or carpet as i did and import a background picture or movie. Last you choose from the Transition Effects one of the chroma effects and play about with it. Voila, finish is your homemade bluebox effect. Have fun.
Here are just some demos i did:
1. my first experiment (dont miss the funny scenes at the end)
2. this I did for my friends at: http://www.dahab-realestate.net
3. its paul 11 years old, telling about his life.