The wireless modem should plug straight into the phone line in the same way that the BT one does. Some wireless routers have to plug into the existing modem, but most new ones have a modem built in. Basically, do away with the BT modem and use the wireless one in it's place. Connect it to the main PC with an Ethernet or USB cable first to check it's connected to the Internet properly. Then once you get a connection you can set up the wireless connection on both laptops.