A VNC client (available elsewhere for Windows, Mac, Linux, others) shows you what's on the remote Haiku computer's screen and sends keystrokes and mouse actions over the Internet. The VNCServer software running on Haiku uses that client data to simulate button presses on a fake keyboard and movements of an imaginary mouse. n the opposite direction, VNCServer scans your screen for changes, compresses the resulting graphics data and transmits it to the client.
This is a port of VNC using RealVNC's version 4.0 final source code (which has an extremely well designed class structure, making it easy to do this port). There are lots of VNC clients out there, but I can recommend the RealVNC ones as working very well under Windows. You can get their clients, servers and source code at http://www.realvnc.com/