Parts of this answer comes from: How do I feed Skype a prerecorded video?
Sure you can.
You can use the Webcam Studio, which will allow you to use pre-recorded media, such as images, audio/video, etc. as a source to create a virtual "bridge" between your live streams (webcam, digital cameras/players, etc.) and other media.
I have used this for both Skype and Flash/Web Based Services like Ubiqq (http://www.ubiqq.com) and Ustream.TV (http://www.ustream.tv/) As shown in the provided screenshots.
This screenshot shows the usage of the Virtual Video Device from WebcamStudio on ubiqq. Which is a flash/web based video conferencing system.
Webcam Studio will allow you to choose both live and pre-recorded media, and enrich it with effects which includes animations, text, and further more.