Welcome to the CentOS fora. Please see the recommended reading for new users linked in my signature.
Anything in the directory, such as symbolic links, that might trigger an attempt to automount something that is not available, causing ls to wait until the mount request times out?
OT: Don't use obsolete/unsupported releases - 5.7 is the current release. See the CentOS 5.7 Release Notes
for details. By not updating you are implicitly accepting that you will live with numerous bugs and security issues (and associated known exploits) that have subsequently been fixed.