What you need depends on how far apart the pcs are. If you want to network them for games, the best way is to use an ethernet cable.
You can only use one adsl router to connect to the internet at any one time unless they are both on separate phone lines and you have 2 broadband accounts. You can connect them together and use one of them to connect to the internet or, for simplicity sake, only use one and connect both pcs by ethernet cable.
If you want to take full advantage of the mobility of a laptop, but still have it connected on the network, you might wish to consider setting up a wireless connection; to do this, you will need at least a wireless infrastructure point and a wireless card for the laptop.
You can connect the 2 pcs through this network for games; you will have the option to allow or disallow their access to the internet.