hiya ash-smith, welcome back
ok, ignore the router for a second.
have you been able to register yet, on either pc? this is the important bit, because it does not register the mac addy of the pc like you said (thats for people conecting via STB) , rather it registers the mac addy of the cable modem. so once the modem is regged, you dont have to worry about registering the pcs/router behind it.
what im saying in a roundabout way is you dont need to run the cd on either pc.
as you have a router im assuming you have ethernet ports on both pcs? you should be able to plug everything in, setup up the router, then reboot the lot, and you should be online - so long as you have already gone through the registration....
(to register without the cd, go to autoreg.autoregister.net and follow the instructions)