Trying to hook up my comcast hd cable box , my vizio hdtv and my panasonic sound system using hdmi cables. The sound system has only 1 hdmi connection out. Does this mean I have to use an optical cable somewhere and if so from the cable box to the receiver and then the HDMI from the receiver to the TV?

Depending on the cable box you can do HDMI out from the cable box, HDMI out from the sound system (assuming it's a blu-ray or upconvert dvd player), and yes, fiber optic out from the cable box in to the sound system.