I have a Compaq Vista Home Basic desktop set up to a Linksys router for my PS2, PS3 and Wii. I want to set up a second desktop computer (Windows98) that will be wireless also. How do I do that? Thank you.

A win98 machine will likely have a rg-45 plug in the back, it's unlikely that may come with wireless network card. just use a straight through cable (the typical network cable) to physically connect the win98 machine to your linksys router, if you don't have any special security on your router, your win98 should be connected after a few seconds.

if you are getting a network card (possilby wireless):
install a network card on your windows 98 computer. if you're buying one make sure in the package says that it is supported by win98 (most are supported in win2k, xp, vista and 7 now so look closely before buying),

if you already have a network card and you are trying to install it, look for proper drivers from the network card manufacturer (drivers need to match model number and operating system(win98)). install your network card as per indicated in package or website if you are downloading drivers.

if you are connecting wirelessly, assuming that drivers are properly connected look in the network manager you just installed and look for the network name for your linksys router (whatever you configure that to be when your first install the linksys router) and attemtp to connect providing a password or any security requested.

in a nutshell that's what you need to do!