If you want to set up a new LinkSys wireless without all my current bells and whistles, see my basic setup info here.
It's set up to work with Earthlink DSL. I have a Powerbook (TiBook500) running OS X 10.2.8 Jaguar, which I connect either wirelessly (Airport card) or docked via Ethernet; and a eMac 1.25GHz running OS X 10.3.4 Panther connected via an ethernet cable to the LinkSys. I also have an older PPC 8600 running OS 8.6 connected to the router by an Ethernet cable. Lastly, there's a long Ethernet cable running to a remote Airport Base Station (Snow) and Windows 98 PC at the other side of the house. The Airport Base Station is only running as a bridge, so it doesn't really figure into this setup topologically.
Accessible from the Linksys Admin web screens (Use a browser to view URL http://192.168.1.1)
The OS X 10.2.8 Powerbook is set up for a static IP address (192.168.1.20) on the LinkSys subnet
The OS X 10.3.4 eMac is set for a static IP address (192.168.1.24) on the LinkSys subnet so I can set up the port forwarding for file sharing, web server, and BitTorrent. Since I use DSL, I've also customized my MTU size to 1492 to allow FTP uploads.
My Airport Base Station is set up as a simple Bridge with DHCP disabled ("Distribute IP Address" unchecked). I've run the uplink from the LinkSys to the LAN port of the Airport Base Station. This lets the LinkSys control the entire network as a single subnet.
I have a quick checklist for configuring a new LinkSys network (without all the above complications) here.
