Since Digium uses CentOS 5.3 as the basis for their AsteriskNOW distribution, it is now trivial to install QueueMetrics on it.
Just type:
wget -P /etc/yum.repos.d http://yum.loway.ch/loway.repo
yum install queuemetrics
Then follow on-screen instructions.
The only difference from a TrixBox installation is that the default MySQL password is blank, and not "passw0rd" as it is on TB systems.
You can find the latest AsteriskNOW here:
http://www.asterisknow.org/node/48579