Well if you have somehow managed to not boot it up for the first time yet there is a walk through for it.
If you already have the account set up I can walk you through everything.
Here are the basic steps if you have the admin account set up.
1. Open system prefs
2. Click the Network button
3. Make sure the cable is plugged in
4. Click the "Built-in Ethernet" section and click Configure
5. The rest is pretty much dependent on your ISP, unless you have some screwy set up it should just work. If you have PPPoE just fill that tab out after clicking Configure and you should be golden.
6. Make sure you turn the Airport off(just drains the battery quicker if you aren't using it) To do that there is symbol in the upper right hand corner near your battery display that shows your wireless signal, click and hold until a list comes down and turn it off.
When you get back we can talk more about customizing the system.