since you already have a wired network all you need is a open port on the switch,hub or router and plug in an
access point
of course if you have an A or G card you would get a A or G access point to support the speeds
just noted if you want to share off DSL and dont have a router already you would get a wireless/wired router which is designed to handle wireless communication and has 4 ports on the back of the router for a wired LAN too