Clearly, the equipment you need depends on how you want to set up your network.
If you are planning to add Wi-Fi to a wired network, in addition to all the equipment you need for the wired network, you need a Wi-Fi access point.
If you are not adding Wi-Fi but rather planning to create a completely wireless Wi-Fi network from scratch, you need a Wi-Fi router to connect to your modem. You can buy a DSL or cable modem that is integrated with a Wi-Fi router as a single unit.
You should also know that you can buy a single unit that works as a router for both wired and Wi-Fi computers. See Chapter 13 for more details about this option.
In either case, you'll need Wi-Fi capability on each device that you want to connect to the Wi-Fi network. This can be achieved either by adding a Wi-Fi card to the device, or purchasing devices that come integrated with Wi-Fi already on board.