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You will need a wireless router : http://www.dlink.com/products/?pid=6&sec=0
And also a wireless PCMCIA card for your laptop : http://www.dlink.com/products/?pid=11
That is the combination I use and its pretty robust.I use cable for my broadband for ADSL you may need a different router.
Basically the router will need to be configured with your username and password for your connection to the ISP.After that is working you set up your wireless connection on the router and assign a security key, usually a certain amount of random characters.You then set up the wireless PCMCIA card on your laptop with the same numbers and tell it to connect to your network.The card and router will then check the numbers against each other and if they match you will be assigned an address and you can connect.
Thats a very simple explanation of it but it is pretty straightforward when you start setting up.Just make sure you turn on the security.
It is very important that you use key encryption otherwise anyone within range of your router will be able to access your network.