Actually, it's all perfectly simple, but since I have no idea how much you already know, I'll assume you know nothing and hope I don't insult your intelligence. As Judland said, you'll need a wireless router and a wireless network card for each device you want to put on the network. The wireless router and cards you'll find described as supporting standards called 802.11b or 802.11g, or both. You want the 802.11g, it has longer range and better speed. Those numbers are just document numbers in a system of specifications defined by the IEEE, the Institute of Electrical and Electronic Engineers.
Your high speed internet connection will come with either a cable modem or a device called a CSU/DSU, but that doesn't matter to you. It'll just be a little box with two cables coming out of it, one of which goes to your Internet service provider and should be connected by the installer, the other connects to the network port on the wireless router (or to your computer if you have only one device and no router). It should be clearly labelled as the network port, and will most likely be on the back of the router. The router's likely to have at least four wired network ports on the front of it as well; those are for your devices, if you want to wire them directly. And there'll be one or two little antennae on the router as well.
The router will have documentation with it, probably on a CD, about how to connect workstations to it, and if you have Windows 2000 or XP, it's pretty much automatic. But read it anyway. If you have trouble, come back here with questions, or PM me and I'll do my best to help you out.
There are some security considerations as well. If you leave the router unsecured, which is likely to be the default setup, your neighbours could use your Internet connection and possibly tap into your computers, so at the very least you should configure it to respond only to the devices you have, according to what are called their MAC addresses. That's for Media Access Control, a hardware address built into, and unique to, every network card. You can also set up encryption between your devices and the router, which will be explained (probably badly) in the documentation. But again, come back here or feel free to PM me if you run into trouble. I've been running a wireless network at home for two years, and never had a problem. I'm also paranoid about security, as we all should be with today's Internet, so every PC here has a software firewall and active virus monitoring, which you should install as well.
And just in case you're worried about my credentials, I used to make my living doing this kind of stuff, so I know what I'm doing.