Do you have a modem? Look at the back of it. Are there any duplicate Ethernet ports? Some modems have built-in routers that can hook up to multiple PCs or a LAN.
If not, you'll need a router. A wireless one is the best for laptops so you can move around. You don't need $100. $50 or less can buy a good wireless router. Look for 802.11g. Dlink, Linksys, Belkin are a few good brands. Also, your laptop needs a wireless 802.11g card. Can be had for $20 or less. Avoid chain stores unless it's on sale. After you get it, post back.