Following relatively recent improvements in the Linux wireless stack and driver support it is now possible to setup a Linux machine as an access point, even if you don’t have an Atheros chipset (which was historically the case). Support is patchy but I would say there is a good chance you can do this if you have purchased a laptop with built in wireless in the last 2 years. It is even possible to set one up with a USB wireless adapter (which even Madwifi couldn’t do) if you have an Ralink chipset.
Why would you want to do this? Well, there aren’t that many reasons considering ISP’s routinely hand out wireless routers these days, but I will give you a couple:-