There are many ways to do this, but finding good turorials about mixing web 2.0 media sources can be challenging. Our friends at Discovery Education presenting "Media Mashups" this summer and have just put up some of their turorials and examples onto the Discovery Education blog. Hall Davidson posted this with lots of links to their downloadable instructions and online examples. It's really an incredible resource.
This video is from Hall and Steve Dembo, from Discovery Education, and it gives a great example of a high-level mashup as well as good background about Web 2.0. This comes from a six part video series for educators about Web 2.0.
--Instructional?--Our Innovation Stations can not only display the products that the students create, but the document camera can help capture stills and videos that can be used in these products. The Discovery blog linked to above gives tips for making green screen videos. For a large flat green screen, how about making a chromakey-green slide in Powerpoint and projecting it on the screen?
How else could you use your IS to make a Mashup?