Just want to let you know, I tested iRedMail-0.7.2 with Scientific Linux 5.6 today, and it works fine (both i386 and x86_64).
Installation guide is available here: http://www.iredmail.org/doc.html
Kickstart file is available too: http://iredmail.org/files/ks/centos/5-latest.ks

iRedMail now works on 7 major Linux/BSD distributions:

- Red Hat Enterprise Linux 5.x
- CentOS 5.x
- Scientific Linux 5.x
- Debian 5.x, 6.x
- Ubuntu 8.04, 9.04, 9.10, 10.04.x (LTS), 10.10.x, 11.04
- openSUSE 11.3, 11.4
- FreeBSD 7.x, 8.x

Enjoy.