Zimbra and apache proxy on diferent servers

[acon]

I have a zimbra host installed over ubuntu 8.04 server. It has only 1 nic with a private address. My network is connected to internet througt another ubuntu 8.04 server, as a gateway firewall, apache sever.
I want to open ports 80 and 443 only to my gateway apache web server.
I need to proxy connections to zimbra server with my apache server, using mod_proxy.
I have followed tis article:
Provide HTTP(s) Integration with Apache - Zimbra :: Wiki
Using virtualservers.
Here is my site file:
<VirtualHost *:80>
ServerAlias correo.*
ProxyPass / Domain Name Registration, E-mail, Web Hosting
ProxyPassReverse / Domain Name Registration, E-mail, Web Hosting
ErrorLog /var/log/apache2/correo-error.log
</VirtualHost>

Ven i reload apache i get:
[Sat Nov 08 13:32:31 2008] [error] VirtualHost *:80 -- mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results.

My zimbra box internaly resolves to mail.mydomain.com.
I would like to use externaly correo.mydomain.com or Domain Names, Shared Web Hosting and Site Design Tools - MyDomain.
All i have read in zimbra wiki is for zimbra and apache on the same box.
Any advice to do it with 2 boxes?
Thanks

[acon]

Finaly y have configured this way:

ProxyRequests Off
ProxyPreserveHost On

<Proxy *>
Order deny,allow
Allow from all
</Proxy>

ProxyPass /correo http://192.168.1.2
ProxyPassReverse /correo http://192.168.1.2
<Location /correo>
Order allow,deny
Allow from all
</Location>


But now, when i go to Domain Names, Shared Web Hosting and Site Design Tools - MyDomain, y get a html login page.
If i try to log in, i get 404 error.

Can anybody help me with this?