1. Switch everything off
2. Unplug all Ethernet cables currently running
3. Plug Cable Modem Ethernet Directly into Router WAN Port
4. Connect each PC to the router's switch (doesnt matter wich port, 1&2 will do nicely)
5. Boot the cable mode, the router, then each of the PCs. Assuming everything is set up in the router already (most are) you should immediately have internet connectivity on each PC (some routers might need configuring, read the instruction manual for instructions on how to do this)
Meh, too slow