Zimbra doesn't use the http daemon. I don't know why it's tied to the zimbra user.
Code:
su - root
cd /etc/init.d
./httpd stop
rm -rf httpd
su - zimbra
tomcat start
Tomcat is our servlet. It binds to port 80, and can't start because for some odd reason, httpd has started. Stopping it, and starting tomcat will fix it.
Good luck!