Speak to your ISP to see if they support setting up your connection with Linux. There are also several web sites available that will help you in setting up your connection.
http://linuxnewbies.editthispage.com/tips/20020219
http://en.tldp.org/HOWTO/HOWTO-INDEX/networking.html#NETPROTOCOLS
http://oob.freeshell.org/nzwireless/LWAP-HOWTO.html