I just performed an installation of Zend Optimizer which is a free runtime application that enables php to run files encoded by the Zend Guard running on a server.

You can download it from
http://www.zend.com/en/products/guard/downloads
Selecting the proper Package.

Download it through shell

wget http://downloads.zend.com/optimizer/3.3.3/ZendOptimizer-3.3.3-linux-glibc23-i386.tar.gz 
in my case i m using x86 32 bit version

untar the package

tar -xvzf ZendOptimizer-3.3.3-linux-glibc23-i386.tar.gz

Go to the directory

cd ZendOptimizer-3.3.3-linux-glibc23

start the installation by running

./install

A welcome screen appears with terms and conditions.

Installation directory: /usr/local/Zend

Location of php.ini
by default it comes as /etc/php5/cli

But it has to be /etc/php5/apache2
(*depending upon your apache installation and linux server*)

The installation process will relocate php.ini file from /etc/php/apache2 to /usr/local/Zend/etc

A symbolic is created for php.ini in /etc/php5/apach2 pointint to /usr/local/Zend/etc/php.ini
php.ini -> /usr/local/Zend/etc/php.ini

If anything goes wrong with the installation , the old php.in is backed up during installation by zend automatically in /etc/php5/apache2 [ which is named as php.ini-zend_optimizer.bak ]

if YOU are not too sure ,YOU can always make a back up of this file.

to complete the installation , you need to restart the web server.

/etc/init.d/apache2 restart

or you can do it at the end of installation when it prompts to restart the web server

to check if zend optimizer is working or not , you put a small php file with the phpinfo() in it .

when you run that file you will get similiar kind of output as following

This program makes use of the Zend Scripting Language Engine:
Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies
with Zend Extension Manager v1.2.2, Copyright (c) 2003-2007, by Zend Technologies
with Zend Optimizer v3.3.3, Copyright (c) 1998-2007, by Zend Technologies

http://www.linuxweblog.com/blogs/manoj/20080624/zend-optimizer-installation-ubuntu