Wireless-G WRT54GS v4 router:\r\n

You can download the user's guide, installation guide, and most up to date firmware for you router from here. Linksys offers pretty good support with FAQ's that may help you to straighten out the installation. see here for that.
It's not clear to me from your post, but are you trying to network this router with another modem, or are you connecting only through the linksys router? It seems to me the latter is the preferred installation. Unless you have some specific need for another modem, this linksys router can replace your old modem and provide both wired and wireless service. Otherwise, you will probably need to configure the old modem to allow the new router/modem access through the firewall. See here for help with that, and avail yourself of the resources at this site, & this page. In any event, you may wish to consult this article or these links for help setting up a home network with windows. The problem could be with your windows configuration instead of the router. Have you run the wireless network setup wizard on the computer? Are you sure the wireless is switched on? See your owner's manual for details on that.
I hope that somewhere there I've led you in the right direction to find an answer.

I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
If I've managed to answer your question or solve a problem, please take just a moment to rate this post....thanks!

As is typical with PC's, the best idea sometimes is to reset it to factory default. Afterward, simply change the username/password and in the wireless settings enable a form of WPA security settings. Don't use WEP, it's too easy to crack (within minutes) by someone sitting outside your home in their car. Never hurts to reset the cable/dsl modem either (unless your wife is talking to her mother and you disconnect her).