having a wireless network is your answer. You need a wireless router connected to the cable modem and the upstairs computer. The downstairs computer needs either a USB or PCI wireless card. The computer running Windows 98 won't have USB 2.0 ports unless you have added them. That might make using a USB wireless connection a bit slow.
I have a Linksys setup. It works well, is easy to install and use. I'd suggest which ever you buy, get all of the components from the same company.
i have a computer set up upstairs in my home.i have a dell 4700 with window xp home edition. ihave a cable modem up stairs. down stairs i have sony with windows 98. how can i hookup the down stairs computer. it does not have to be wileless can anyone help me get started thanks