You can connect them with an ethernet cable, or by WiFi if they have wireless cards.
You can use wireless network cards to connect two computers to the same network so you can play computer games. Another way to connect two computers is to use a crossover cable between them using the Ethernet ports so they see each other and assign an IP address.
you can play player vs. player on nba2k11 by just plugging in two controllers then go to quick game and there will be one red controller and one blue controller on the screen
Two computers
Best way is to connect both computers to the same computer network (within the same router, or switch). You can also connect them directly using a crossed patch cable, or wireless by creating an ad-hoc Wi-Fi connection of these two computers (if both have Wi-Fi adapters).
a cord
You can buy a firewire cord. That is the fastest and easiest way to connect two computers.
wireless
An HDMI cable is not designed to connect two computers together.
yes
Cross cable.
linksys
Buy a lan router, they can be used with lan cable or wireless to connect all your computers through a network. If there are only two computers that you wish to connect then you only need on lan cable which you connect in the back of each of those two computers to create a network.