Adding wireless to home LAN w/ WRT54G2

Question

I have a home LAN composed of ethernet cables and two Linksys Etherfast 10/100 5-port workgroup switches. This setup is about 6 years old and has always worked fine, has never been updated since original setup.
Now I need to replace the ethernet card in my son's desktop computer, and since he will probably be getting a laptop soon with wireless, I figured this would be a good time to add wireless to our network. I've never worked with any wireless network stuff before, so just bought what the guy at Staples recommended: a Linksys Wireless-G PCI card to replace my son's ethernet card, and a Linksys WRT54G2 Wireless-G Broadband Router.
We are not using the Router for an internet connection; we live too far from town for cable, and don't want Embarq DSL, so our only internet connection is by dial-up through my computer (connection shared with the kids through our LAN).
All I want this new wireless stuff for is to let my son connect to our existing LAN via wireless.
Problem 1: all of the setup instructions seem to assume that we are connecting to the internet by cable or DSL and that this will go through the new router. As noted above, we're not doing that.
Problem 2: when I try to do the initial setup from the included CD, it keeps giving me errors. The errors are different depending on whether my computer is connected to the internet via dial-up when I run the setup:
2a) if my computer is connected to the internet via dial-up when I run setup, the error message comes during the first step (Check Connection) and says "Error 301: Internal Error" - unfortunately, there does not seem to be any reference for me to look up Error 301 and see what this actually means.
2b) if my computer is not connected to the internet when I run setup, then setup progresses OK through the Check Connection step without error and goes on to the Install Router step. Since I am not connecting to the internet through this router, I cannot follow the instructions exactly as given (since they assume a cable or DSL connection through the router), but I do the rest of it and connect the router to my computer's ethernet port with the included cable, then plug in the router. Setup shows a "waiting for router" message for about two minutes, then terminates with the error message: "Your new router does not appear to be connected properly. Error 322: New Router Not Detected." (The green LEDs light up showing that the router recognizes an ethernet connection in LAN port 1, but the setup program doesn't seem to be aware of this somehow?)
Problem 3: I thought that I might be able to just skip the above by giving my web browser the address 192.168.1.1 and going into the router's internal setup that way. No such luck; although the router is connected to my computer and is powered on, my browser says the requested page is Not Found.
Is this even the right product for what I am trying to do - add wireless to our existing LAN? Or is this only intended for connection through a cable or DSL modem to the internet,as all of the instructions seem to assume?
Any help for dealing with above error problems and getting this thing working?

Answer 1

You did not want a wireless router. You wanted a wireless access point. Wireless routers are made to share the internet connection. That's what the standard installation procedure on the CD does. Anything else must be done manually.
You can use the access point in the WRT to add wireless to your existing LAN. The basic instructions are here.
In your scenario the first router is your dial-up computer with internet sharing. It uses IP address 192.168.0.1 by default. An available LAN IP address for the WRT would be 192.168.0.2 with subnet mask 255.255.255.0.
To change it, you should unplug the WRT from everything. Connect a single computer by wire to the WRT. Do not use your dial-up/internet-sharing computer for that. This other computer should automatically get an IP address from the WRT and now you should be able to access http://192.168.1.1/ In the setup change the LAN IP address from 192.168.1.1 to 192.168.0.2. On the same page also turn off the DHCP server. Now save the settings. You'll loose the connection.
Now rewire everything back. The WRT is hooked up by one of its numbered LAN ports to your LAN! Do not use the internet port of the WRT! That should do it. Now wireless computers can connect through the WRT into your LAN and through that to your dial-up and internet.