Free good video editing software?

I watch HBO's TRUE BLOOD religiously, and the format is as follows:

1) Show opens and goes on until there is a surprise element
2) Cuts to title and theme song
3) Theme ends and show continues
4) Ends on a cliffhanger
5) Following show picks up from last show's cliffhanger scene; process repeats

I want to make the episodes into a movie. Nothing fancy, I just want to isolate a title scene, move it to the front of the film, and link all the episodes together into a larger file. Make it look more cinematic.

I have all of the first season in AVI format.

What's some good free software to edit clips together? Windows Movie Maker won't allow me to add more than one video stream like I'm thinking I need to do; at least not one that would allow for clean editing. I'll probably need to trim frame by frame, to remove end credits and streamline the different videos.

I'm a complete noob to all of this stuff, just playing around. I thought getting into editing might be something I'd enjoy.

Any help is appreciated. Thanks to all!