I had this issue also in CentOS 5.2. To give a little back ground on my installation, when i tried to install first i had a dns error and a port conflict error on port 25.
To resolve the dns error i created a split dns setup as per these
instructions, i needed the split dns because i am behind a isa proxy server, and because i do not have dns entries for my domain on the internet.
To stop the port conflict, i just needed to stop the sendmail service.
when i tried to install after these steps, the setup hung after the "initializing documents .." step.
To solve this i followed the suggestion in this thread to replace the entry in my /etc/hosts file with "127.0.0.1 localhost.localdomain localhost domain actualhostname"
Im not sure if the /etc/hosts file got corrupted during the setup but after fixing it zimbra installed correctly.
Steve
web design ireland