At last i was able to install a Rapid Freessl cert into Zimbra NE 5.0.8 Centos 5.2
Amazing!
I got only this serror:

httpd: Syntax error on line 232 of /opt/zimbra/conf/httpd.conf: Cannot load /opt/zimbra/httpd-2.2.8/modules/libphp5.so into server: /opt/zimbra/httpd-2.2.8/modules/libphp5.so: cannot restore segment prot after reloc: Permission denied
This error is a know bug, you can find it in bugzilla

[192.168.30.5 18:17:59 zimbra@zimbra ~/freessl ]$ sudo zmcertmgr deploycrt comm commercial.crt commercial_ca.crt
** Verifying commercial.crt against /opt/zimbra/ssl/zimbra/commercial/commercial.key
Certificate (commercial.crt) and private key (/opt/zimbra/ssl/zimbra/commercial/commercial.key) match.
Valid Certificate: commercial.crt: OK
** Copying commercial.crt to /opt/zimbra/ssl/zimbra/commercial/commercial.crt
** Appending ca chain commercial_ca.crt to /opt/zimbra/ssl/zimbra/commercial/commercial.crt
** Saving server config key zimbraSSLCertificate...done.
** Saving server config key zimbraSSLPrivateKey...done.
** Installing mta certificate and key...done.
** Installing slapd certificate and key...done.
** Installing proxy certificate and key...done.
** Creating pkcs12 file /opt/zimbra/ssl/zimbra/jetty.pkcs12...done.
** Creating keystore file /opt/zimbra/mailboxd/etc/keystore...done.
** Installing CA to /opt/zimbra/conf/ca...done.


You should use cli instead of gui.
with gui i got errors.

The problem:
every time a client send out mails using mailman to more than 100 subscribed account, qmail stop to work.
Analisys.
Issue is due to inetd. I have debian etch and inetutils-inetd installed.
To avoid mailman issue, the fix is:
smtp stream tcp nowait.max
where max is a vaery large number

BUT:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=451478

inetutils-inetd does not support nowait.max

you MUST use openbsd-inetd

do not use xinted as plesk do not provide /etc/xinetd.d/* files, you have to do them yourself