I am using Fedora Core 6 with vnc-server 4.1.2

when I run vncserver command, the server seems normal. I can see a process
Xvnc and a listen port 5801.

but when I run RealVNC viewer 4.1.2 another computer of Windows, the
connection is always failed.

I added an ACCEPT rule in iptables enable the port 5801, but it made no
effect.

I don't know why. Who can help me?