Live stream set up: use of multiple cameras, switching between them, adding graphics

I belong to a paranormal investigation group and we are planning to stream our investigations live over the internet to our members on our website.

We plan to use two DV camcorders and would like the use of switching between the two (i.e. video mixing) and also have the option of adding graphics to the live feed (almost like a Directors Gallery). What software would I need and how would I set this up.

I know that I would need firewire which I have the relevant cables, I also have a streaming site that will stream the live feed, it is just the use of multiple cameras, switching between them and adding graphics. Any suggestions?