Ok it looks like we are dealing with the Linksys WRT54GS. It is a 4 port router with 802.11g and up to 128 encryption...
Ok Bobo here is the deal... the wireless adaptor is only supported in windows 98SE... If you have a ethernet connection to that pc it should work fine... You also might want to make sure that if you have the WEP enabled, HIGHLY RECOMMENDED!!, that the key code match on both ends. Otherwise you will not be able to connect to the router... Linksys doesnt support windows 98 standard edition for some reason... My guess is that all of the wireless networking stuff was first included on windows 98se.... You could try to do a windows update... I think that Microsoft might have discontinued Windows 98 support...

Otherwise move this computer to the router and use an ethernet connection... An use the wireless card on some ME/2000/XP computer.. Good Luck!!