Vncviewer doesn't run Windows on the N810. It allows you to remote control another computer that is connected to your network.

You need to download, install, and run VNC Server on the Windows PC that you want to remote control. Then run X Terminal on the N810 and type vncviewer on the command line. After vncviewer starts, you need to enter the IP address of the Windows PC that is running the server. You can find out the IP address by holding the mouse pointer over the vncserver icon on the task bar of the Windows PC. Once connected you should see and control the screen of the Windows PC on the N810.