This is the first time I've run across this, but I usually work with TWC and Verizon where as long as it is a supported modem they don't care (or they don't charge you for the modem). I can't believe ...
Anyway, call Comcast. There should be a static IP assigned to you, everyone I know who has requested this gets one. I had one for three years. Use that IP# for your network settings and you should ...