Considering the computer is from the 20th century, you might also need a NIC (Network Interface Controller) card that will run right off a PCI (Peripheral Component Interconnect) slot (This unless ofcourse you already have a etherport on the back of your computer to connect to; it might be built on your motherboard already). There are an assortment of brands that make these cards now, Etherlink from 3Com is a good buy though. They now usually come with the option of wireless connectivity built in, so you can run both hard-wired and wireless networks. Alltogether this wireless project should run you about $100.00-$150.00 dollars max. You can do it hard-wired for about $20 dollars less. Check out
Newegg for good pricing.