yea read that guide so you understand better, but one thing i just want to make clear. However you download from the internet, whether modem or cable, etc makes no difference to however you will connect to the xbox and the speeds you'll see there. And the easiest thing for you to do is to buy a crossover cable and connect to the xbox that way, no router needed.
oh and for your what is a NIC question, try using google for some things. You'd find this:
What is a NIC
