Need more info than that. Do you have a router, or do you want to just use your PC (or a second pc that you own) to run some internet connection sharing. 2K OS I assume, seeing as we are in that section.
You can figure out your ip by going to ipcongig in the command menu. (not to talk down to you like you knonw nothing, but just incase you have no idea what I'm talking about go to the start menu and the go to run. type "command" in to the box that pops up. Once the comman prompt comes up type in "ipconfig" and then hit enter. You will then be able to see your ip address.)
Depending on how your cable modem is set up, like if it only has an rj45 connection and not a usb connection (& you don't have a router.) One of the easiest ways is to run your PC with 2 network cards and then run internet connection sharing from your pc. (One note if you do it that way, remember to hard set the ip of the card that will be connected to the lan.)
If you have a router set up it'll just be plug and play, as long as everyone is set up to obtain an automatic IP. As far as seeing everyone strait out in network neighborhood, it's a whole lot easier if all of you switch to the same workgroup (although it is not really needed.)
GOOD Luck and I hope you enjoy