You really need to turn the router upside down and read the stuff on the bottom. Or go to Belkins website and compare pictures. We also need to know what OS you are running on the 2 PCs.
Your problem is you havnt properly set up your network.
And for your question, NO you cant just go get a cable modem, plug it in and steal interent. Each modem has unique number called a Mac address. The cable company only allows KNOWN mac address on the internet...
If you did do this you would have to pay double.
And last but not least, their is a web site called
www.google.com Type in what you want to know about and it will give you about eleventy billion responses... Their is a catch though, you have to read.... HEHEH Just giving the noob a hardtime.
Seriously, get that info back in here and we can help you to do this the right way....