First of all, you need to find out if your laptop has a wireless network card installed. This card will allow it to connect with a wireless modem/router in the next room without a cable.
To find out if your laptop is wireless enabled, check in device manager in the control panel of the laptop, or better still, have a look at the manual.
If a network card is installed, you then need a wireless modem/router. Here's a good one assuming your Broadband Connection is ADSL and not cable:
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Now normally, you would put this router near your main computer and connect the two via an ethernet cable. Your laptop on the other hand would be connected wirelessly.
If you want both computers to be connected to the modem/router wirelessly, you need a wireless "key" which is a small device that sits on a stand out of sight near your main computer. The key is plugged into the PC USB socket. This key will pick up the connection wirelessly from the modem/router just like the wireless network card in the lapop and connect the PC to the internet without cabling in sight.
Every modem/router comes with an ethernet cable in the box. Wireless keys are sold separately sometimes, but often you can buy a modem/router with the key included in the pack. Many of the Belkin modem/routers include a key virtually for free when you take into account special offers in the shops.