Well this is on my to do list but kind of far down, but I think it is possible with the commerical product VHI studio. My biggest worry is that my web cam is a par. port type, but I think my add on ser/par. card can emulate the pc par. signaling without a problem. USB webcam should be easy and I even think some of the USB cards may have something basic to at least get the web cam up and running though not doing anything special. Not much info. but at least you know you are not the only interested party. ;-)
