Well, does the file lib-common.php exist (in the same directory where your index.php resides)? This doesn't seem to be a problem with path settings - either your index.php is in the wrong directory or the lib-common.php is missing.
Also, you shouldn't install Geeklog 1.3.7rc1 - that is a beta version. You want Geeklog 1.3.7-1.
bye, Dirk