You need to get a wireless access point/router, connect it to your modem.
The router will then have plugs in the back for your desktop to physically plug into, and antennae to broadcast wireless in your home. Then you can access the internet anywhere in your house with your laptop.
Here is an example of what you are looking for, there are many, many types, and costs. This one is a pretty popular less expensive model and would probably suit your needs quite well.http://www.newegg.com/Product/Product.aspx?Item=N82E16833127256