This directory (and version of CentOS) is depreciated. For normal users,
you should use /4/ and not /4.5/ in your path. Please see this FAQ
concerning the CentOS release scheme:

http://www.centos.org/modules/smartfaq/faq.php?faqid=34

If you know what you are doing, and absolutely want to remain at the 4.5
level, go to http://vault.centos.org/ for packages.