Attention: in order to get this plug-in to work in 2.7+, you have to make a small adjustments in 'stattraq-install.php'.
You can fix the problem of the missing ABSPATH declaration (actually it's defined in wp-config.php ^_~) by replacing 'ABSPATH.' with a normal variable containing the path to your blog installation.
$path = 'http://your.wordpress.url'; require_once($path.'/wp-config.php');
Please remember, if your blog is placed in a sub-folder you have to consider this in the '$path' variable, e.g.:
$path = 'http://your.domain.url/wpfolder';
This is only one possible solution - maybe not the nicest one but a fast, quick and dirty trick to make the installation work ^-^