Separate LAN and WLAN (outdated)
From DD-WRT Wiki
While Linksys never intended their WRT54G/GS router to allow multiple local networks, it is possible to separate the WLan network from the Lan network and allow both to independently access the internet. Since this was not supported by the original Linksys firmware, and all custom firmwares are a derivation of this, performing this setup will yield some somewhat unexpected results when configuring certain options from the Web Interface. (For example, advanced Routing from the Web Interface, when directing to the WLan