[Halcyon]

As has been mentioned you dont need the installer disc.
First connect up your first PC directly to the cable modem and once the Internet is working there, then you can go and sort out your network.
To set up the network once you have net access turn everything off including the modem. It should be as plain as plugging the cable modem into the router, and then switching it on first, then the router.
Then use the routers setup disc or instructions to set up each machine.
Good luck.