The Netgear box and the Comcast box are NOT "real" routers. They are NAT Firewalls.
If you want to route between the networks you need a "real" router. The simplest and lowest cost would be a Layer3 capable switch. However this requires knowledge and skill to know how to setup such a thing.
The simplest thing for you do to is have two Nics in the PC. On the second nic plug it into the Camera LAN. Do not use DHCP on that Nic. Statically assign it an IP and a Mask. Do not give is a Gateway. Do not give in any DNS settings.
