I found this page while looking for VNC options on my new CentOS server and decided to give x11vnc a try. I have already had several occasions while I was sitting on my couch that I wished I could log into the X session that I already had running on the monitor in the other room. This program gives me that option. In a nutshell, I downloaded the RPM, installed it and ran it. Poked a hole in the firewall and was immediately able to view my X session from my laptop.
Downloaded the RPM from http://dag.wieers.com/rpm/packages/x11vnc/.
Installed using rpm
rpm -i x11vnc-0.9.3-1.el5.rf.i386.rpm
Run the program
x11vnc -nopw -display :0.0
Open the port in iptables
iptables -I RH-Firewall-1-INPUT 15 -p tcp -m state –state NEW -m tcp –dport 5900 -j ACCEPT
Now I can launch a VNC viewer and connect to the remote X session at 192.168.1.100:0.0. I am not running x11vnc as a service, so it will need to be started every time I want to use it, but I can do that remotely through an SSH session and then kill it when I am finished.