Can we be sure what you have. As I understand it, you have an adsl wireless router, a desktop pc connected to the router by a wireless connection and a laptop that you are trying to connect to the internet through the router.
Can you connect to the internet from the home pc?
Can you tell us the make and model of the router and the laptop's wireless card. Is it a Centrino?
Does the laptop have any wireless management software that came with it? If so, open the software and make sure that it is set up for an infrastructure connection, NOT ad-hoc. The software should find the router and attempt to log on to it.
The software will show you the network address given to your laptop. When you are connected, the address will probably be in the range 192.168.0.x or 192.168.1.x depending on your router. If it shows as 169..... then it means that there is no connection.
If you cannot connect, disable the firewall on the laptop for a short while to see it that gives you a connection.