If you're running gnome, you should get a nice graphical tool if you run "network-admin".
Then you just edit the preferences of your ethernet card, and set it to dhcp, and restart it. Usually you're done at that point. You can then run ifconfig, to see if you got an ip. ping 192.168.1.1 to see if you can reach the router. And if that works, you should be ready to go.
Your router might deny services, but that should be pretty straight-forward too, if you have the password.