It Shouldn't Be So Difficult...
You should understand that it's very difficult to solve these kind of technical issues over the phone. So while the techs you were talking to might not be experts, they were probably doing as much as they could with the information they had from you.
We might be able to help out more here if you provide a few more details about your setup. First off, you didn't specify but I'll assume you are talking about an XBox 360, and that you have it attached to the same router that your PC is attached to. More than likely your router is set up to assign IP addresses automatically (DHCP), therefore you shouldn't have to do more than attach your XBox 360 and ensure all of the items on the Network Settings page (on the XBox) are set to automatic. This will enable your XBox to get all the information on IP's, DNS, and subnet mask from the router.
In some cases you might have to reboot the router once the XBox is attached in order for it to recognize the XBox. In any case you should allow a few minutes before testing your network connection from the XBox.
Feel free to post back here if you are still having problems. It might also help if you let us know which ISP you are with and what model router you own.