first of all

to CF (Rob how rude)
okay, the old lappy do you know what kind of card it has in it? as I have seen issues with old B cards that cant find any G network even if its broadcasting B/G.
other thing it could be is that the wlan on it has been disabled and that you have to enable it, this depands on the laptop on how to do this.
there are about 10 things that could be wrong here....also what kind of security are you running on the linksys? if its WPA-PSK then your B card will not connect to it...only WEP it supports.