Ok. You need to install the driver for this D-Link WNA-1330 Wireless PC Adapter Card, then configure the wireless adapter to match the setting on wireless router. You should check the wireless adapter configuration on other working computer in order to know what wireless setting should you configure.

You won't mess up your Sister's 802.11B/G network as long as you don't change the settings on router. You can also take a look on how I set up simple wireless network here, so you can have better understanding.

Good luck..