Do you have the router's wireless settings correctly enabled, i.e. set to B-Only, G-Only or Mixed as appropriate?
Is the router set to broadcast its SSID?
Both of these are configured in the Basic Wireless settings section of the "Wireless" tab. In the laptop, it should then just be a matter of scanning for Available Wireless Networks, selecting the one that matches your router and selecting the option to "Connect" to it. Once "Connected" the Wireless Network Connection should get its IP address and you should have network and internet access.
(I'm currently connected with a WRT54GS and Telewest)