USB/Firewire "Branching" -- Is it Possible?

Shaze asks: "I have been doing a lot of overseas web conferencing lately and have been playing around with my two webcams. I was suddenly intrigued by the idea of being able to 'span' or 'branch' both webcams together to create one device pulling signals from both. I did some quick research on the topic to no avail, however many of my colleagues believe this to be possible. Some even going so far as to say they have seen software or drivers that will turn your webcams into one Twain device. Aside from my own meanderings, I can't seem to find any information on anyone or anything even suggesting this is possible. What do you say Slashdot readers: Is this a new application waiting to be marketed or am I just seeing double?"