Currently no Windows 8 drivers of RTL8187 USB network card are available. You have to wait for some time until they are released. For the time being, you can download Windows 7 drives and try to install on Windows 8. Here is the link from where you can download Windows 7 drivers of RTL8187 USB NIC.
1. Select hardware installed in Device Manager (RTL8187 wireless)
2. With right click on the mouse select Update Driver Software.
3. Choose Browse my computer for driver software.
4. Select Browse and locate the folder named "Driver".
5. Finally wait and Windows 8 will find the driver and install it.