Actually, there are all kinds of things you can do using Windows Movie Maker if you can find the info you're looking for. Check out this site, you'd be surprised of the amount of custom effects and transitions that you will find, including clip overlay.
Windows Movie Maker Forums I wish that I could give you more info than that, but it's been so long since I've used Movie Maker that I can't remember how to add all the custom effects, titles, and transitions. I only know that I've done it in the past, and the site above is where I started my research. Scroll down until you find Movie Maker Users Showcase. You'll find the custom effects there.
Good luck, I hope you find what you're looking for.
