Enabling PHP error logging

Within the PHP directory, open php.ini



display_errors = Off (This will redirect the errors from end users)
error_log = "php_error_log .log"


Then restart the Apache server, you should now find the log file within the PHP folder.

Knowing installed Joomla version

That is explicitly available in the Joomla file:

Joomla Root Directory\libraries\joomla\version.php


var $PRODUCT = 'Joomla!';
var $RELEASE = '1.5';
var $DEV_STATUS
var $DEV_LEVEL
var $BUILD
var $CODENAME
 var $RELDATE
var $RELTIME