The PCI expansion slot is on the motheboard inside of the computer tower. This allows you to plug and play cards of your choice. It it likely that the modem you are using currently occupies one of the slots. NIC card simply means "Network Interface Card". This is a card that provides an ethernet connection (Cat5 cable, RJ45 connector) that cable modems, DSL, routes etc require. This is what you would use to set up a wired network. The wireless I/O card is simply a transciever card that provides a wirless (uses Rf or "radio" frequencies) between the computer and the wireless router you mentioned you want to try to use. It is up to you to decide how you want to go about setting up your network. A wired network is more secure but you must have cat5 cables between the computers and the router. Take a look at the tutorials on that link I provided in my first post. It will give you step by setp instructions about how to set up a network, whether it be wired or wireless. You can get a NIC card or wirless transceiver at any computer store. Walmart even has them.
If you decide you want to go with a wired network, you can get cat5 cable and RJ45 female jacks (with color coded instrutcions and even a punch down tool) at Home Depot. Then use pre-fabricated cat5 patch cables to go from the jack to the computer or router. This method requires no special tools or knowledge of cable color codes and pinouts. This is how I set up my network (4 computers, a router and a cable modem).
Edited by austin_o, 06 January 2007 - 01:37 PM.