1. Make sure you know your girlfriend's ISP login details.
2. Disconnect the existing modem from both computer and ADSL telephone socket.
3. Connect the new router to the phone socket using the cable supplied.
4. Connect the router to the PC's ethernet socket using the cable supplied.
5. Connect the router to a power supply.
Now, on the PC run any software that came with the router. Open the browser on the PC and type in the IP address that is provided in the router's setup instructions. Press the enter key.
This should open a web page that is actually installed in the router's ROM (Read only memory).
You'll need to login to the router's configuration settings using the details provided in the setup instructions. Now follow the instructions to enter and save the ISP login details to the router's memory. Once you've done this you should see the router making a connection to the broadband service, and when that's finished you will be able to access the internet. If the PC doesn't have a wireless network adapter installed you can leave it permanently connected to the router via the cable. If it does have a wireless adapter you may now remove the cable.
The laptop's wireless adapter should now detect the wireless signal from the router. tell it to connect, and you'll be on the internet on that machine as well.
Later, when you have everything working smoothly you might want to go back into the router's settings (via the cable connection) and enable security encryption, so your neighbours can't share your bandwidth.