http://www.realvnc.com/products/free/3.3.7/winvnc.html#11

   [HKEY_LOCAL_MACHINE\SOFTWARE\ORL\WinVNC3]
   "AuthHosts"="-:+192.168:+193.77.104.3:"
   Type SZ

   This would deny all and allow everything from 192.168/16 and from 193.77.104.3/32