PEAR is a collection of PHP extensions.
The adodb is an extension which allows you to connect to many different types of database. It is written in PHP and can be run on any server using PHP. Our server is *nix.
It works on our old server so I am trying to find out what settings could be different and nothing except some very minor PHP and MySQL upgrades (e.g. PHP 5.2.10 rather than 5.2.6).