I have some linux boxes running SuSE linux which uses the Xvnc server. Just to check, I updated all the software this pm, having just bought VNC Viewer.
The server is accessed through an open firewall port with no security - the user is required to log on when the VNC window appears. I can access this server from anything else except my iMac with ease - almost instantaneously.
I set up the necessary info to connect (IP address, port 5901, no security). My LAN is run over Ethernet from my OS X 10.6.4 iMac - one of the linux boxes provides a net firewall and server.
When I ‘check availability’ a blue spot appears on the connection list. When I connect the spot goes to the ‘half connected green/orange’ state; after some few seconds VNC Viewer reports ‘Timed out’. No number of attempts to connect receives anything other than this response. Attempts from other viewer software succeed within a second of requesting the connection.