Check out the linux
Wireless Resources Page.
Especially pay attention to the link to Jouni Malinen's pages, who has developed a driver that should make it easier for you to turn your linux box into a Wireless router, with the aid of a cheapo card using the Prism chipset. Also look at the link to Jason Boxman's pages, which are a guide to setting up your linux box as a Host access point with the aforementioned driver and prism card.
In theory there's no reason why you shouldn't use your linux box as a wireless access point and router, but - if you do - it would also be a good idea to become familiar with iptables (for example) to control who does and who does not have access to your linux box. iptables is particularly nice to use because it allows you to restrict access based on MAC address.
HTH.
