Configuring the router would be a start. I will assume that you have got as far as removing the old modem and plugging in the router via Ethernet cable to your desktop PC. You could plug it into the notebook in this way for the purposes of configuration.
Open a browser and enter whatever IP address is used by BT Voyager routers. 192.168.*.1 where * could 0, 1 or 2. As I don't have a BT manual, you're better placed than me to find that out.
Now setup the router's configuration as per the manual (download one if necessary). Obviously, I won't be able to give you specifics at this point in the proceedings. Another Voyager user might be able to, but I avoid all things BT.
One thing that is bothering me: you say in your first sentence that the notebook has wireless capability, but later state that you have plugged in a wireless adapter. If both those comments are right, then you are going about this the wrong way; if the notebook is wireless enabled, then you are lucky because that is easier to configure and use than an external adapter. Please confirm either way, so that I can advise you further.