I found a great article on installing ZenOss

http://www.installationwiki.org/Installing_Zenoss

It covers RedHat/CentOS, Debian, and source installs. One minor typo I noticed. It has ‘service snmp start’ where it should read ‘service snmpd start’. Also it doesn’t mention you could run ‘chkconfig snmpd on’.

One thing I ran into was a dead PID file from a failed install. I think it had to do with net-snmp-libs not being up to date (another minor omission.) A quick search turned up:

http://www.linuxforums.org/forum/servers/116115-snmpd-dead-but-pid-file-exist.html

Short answer is I had to rip out net-snmp and reinstall.

Still ran into trouble with the RPM install (not prompting?) for things like mysql username/password and port number. You can edit the latter in /opt/zenoss/etc/zope.conf and the former in zenoss/bin/zenoss_init_pre though at that point I just ripped it out and ran zenoss-stack-2.2.4-linux.bin which prompts for the mysql root password and zope port number.

But that hung too!

So I killed it and ran:

/etc/init.d/zenoss-stack start
which complained:

/usr/local/zenoss/mysql/scripts/ctl.sh : mysql (pid 23145) already running

since mysqld was already running

On another VM (CentOS 5.1 on VMWare on Windows instead of CenOS 5.0 on Xen) it started up no problems, however.
The default install is insecure and you should change your mysql, zope, os, and admin logins.