|Your Windows 98 PC must have a wireless adapter installed to start with if you want to access the internet wirelessly from it. The problem with that is that I know of no wireless adapter these days that works on Windows 98 because no Windows 98 drivers are supplied with them.|
That means you will almost certainly have to use a network card instead of wireless on your Windows 98 PC. The network card fits inside the PC and connects to the router with an ethernet cable. Bear in mind though that finding a Windows 98 device driver for the network card may also be a problem.
The bottom line is, Windows 98 is far too old to use for broadband internet. it was okay when all we had was dial-up internet through an analog modem, but technology (and newer Windows versions to support that technology) has changed considerably since the days of Windows 98.