Lucho,
If you really, really want to do this, then here is how I did it on a test server.
mkdir -p /etc/e-smith/templates-custom/etc/httpd/conf/httpd.conf/VirtualHosts
cd /etc/e-smith/templates-custom/etc/httpd/conf/httpd.conf/VirtualHosts
cp /etc/e-smith/templates/etc/httpd/conf/httpd.conf/VirtualHosts/20IbayContent .
cp 20IbayContent 19IBayContent
pico -w 19IbayContent
remove everything after line 28, except the last }
modify the DocumentRoot line and replace $basedir/html with /opt/joomla
Change the ScriptAlias and Alias lines to suit you.
pico -w 20IbayContent
(remove lines 14 - 29) This is what you have in 19IbayContent. If you don't remove these lines, then the last entry for DocumentRoot wins and you will be taken to the default index.html file in the Primary/html ibay directory.
expand-template /etc/httpd/conf/httpd.conf
pico -w /etc/httpd/conf/httpd.conf
search for joomla - you should see that it is now set as the documentroot
/etc/rc7.d/S86httpd-e-smith restart
Open your browser to the servers default page and joomla should come up.
I have the sample data loaded and when I click on an article the url has
www.mydomain.com/joomla/.... appended. If you don't want joomla to appear here, then
pico -w /opt/joomla/configuration.php and change line 10 and just drop the /joomla from the end. At least that's all I had to do.
The only thing you have to look for is if there were any changes made to 20IbayContent from any upgrades, that would need to be updated in your templates-custom directory.
I don't know joomla well enough to do a lot of testing, but that is what worked for me.
If you try this, I'd like to know how it worked out for you.
Good Luck,
John Bennett