If you need to get the wordpress version in your script, there is a global variable:
$wp_version (right now it's something like '3.1-RC3-17376')
It contains the wordpress version.
If you need to acquire if from a file, you can read it from /wp-includes/version.php:
function getWPVersion() {
$path = '/path/to/wp-install';
include $path.'/wp-includes/version.php';
return $wp_version;
}
Wordpress Version Variables
There is more information available in that file:
$wp_version - The WordPress version string ('3.1-RC3-17376')
$wp_db_version - Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema (17056)
$tinymce_version - The TinyMCE version string ('3393')
$manifest_version - Holds the cache manifest version ('20111113')
$required_php_version - Holds the required PHP version ('4.3')
$required_mysql_version - Holds the required MySQL version ('4.1.2')