Zimbra and Munin

[Tripple]

I'm running munin on my Zimbra server but it doesn't work very well.
When running apache from /etc/httpd on port 81 I have a conflict with spell.

If found this post:
Anyone use Munin with Zimbra

I try to do some adjustments to get this working on my server. I guess my htmldir should be:
/opt/zimbra/jetty-6.1.5/webapps/zimbra/munin/

But when I go to:
http://my.zimbraserver.com/zimbra/munin/

Error 403

I know I should change my config file but this file doesn't seem to be the right one:
/opt/zimbra/httpd/conf/httpd.conf

Any ideas?

[uxbod]

Well it would help if you were to update your profile with the following output so we know which version of ZCS you are running

su - zimbra
zmcontrol -v

[Tripple]

Sorry, I forgot that:
Release 5.0.16_GA_2921.RHEL5_20090429052155 CentOS5 FOSS edition