help required with pear on debian

Hi, I've been using PEAR with a selection of packages on my winXP and winNT boxes for about four years. I'm now developing a new site on debian. I've installed php-5.1.2 and have checked it works by displaying phpinfo() without any problems. I have a site that I have been building on my winXP laptop and uploaded to the debian box. Calling the home page gives me the following error: Fatal error: require_once(DB.php) [function.require-once]: failed to open stream blah blah I have tried to find DB.php on my debian box with no joy. I'm very much a newbie as far as linux is concerned. Debian is the flavour used in other sites operated by the company I work for. Can anyone tell me how I can get PEAR sorted? MTIA George