Set up your wirelss NIC first. This varies upon different machine models. Usually a web search would solve your problem. For my scenario (Intel IPW2200 card on Fedora with rpm.livna.org), a "yum install ipw2200-firmware" is enough.
Then the only thing you need to config is your NIC's config file, usually named "ifcfg-eth?". For Fedora it's in "/etc/sysconfig/network-scripts/". Here's mine:
# Intel Corporation PRO/Wireless 2200BG Network Connection
To bring it up, use "ifup eth?".