To be able to use two PCs or laptops on the single telephone line you need to buy a ROUTER.
In your case a WIRELESS ROUTER.
On an ADSL line (which yours is) the router you buy will contain a modem, so you remove the modem from your connection and plug in the router.
Although it is called a wireless router you can also plug a PC or laptop in it via a wire, so it works as a WIRED router AND a WIRELESS ROUTER.
You need to make sure your laptop is wireless enabled (I think any laptop you buy nowadays is wireless enabled).
This article may help:
http://www.microsoft.com/windowsxp/using/netwo rking/setup/wireless.mspx