Before you install PEAR, we recommend you understand what PEAR is and why you should install it.

The base installation that comes with the PHP distribution contains all the stuff that is needed to run the PEAR installation tools etc. If you have a recent installation of PHP, you can relax: The PEAR base installation is already there - unless you have compiled your PHP with the ./configure flag --without-pear.

The packages that do not come with PHP can be installed with the PEAR package manager. The manager handles installation similar to Debian's "apt-get" package management utility, as well as others such as "yum". Again: If you are running a recent version of PHP (> 4.3.0) you can skip the next section. But if you are running PHP 4.2.* or earlier, you need to manually install the manager.

Apart from installing packages, the PEAR package manager also handles some other tasks: It can create new packages on your machine, manage a registry of installed packages, check dependencies and it can interact with services on pear.php.net, and other PEAR compatible channel servers to get information about available packages
http://pear.php.net/manual/en/installation.introduction.php.