For reasons I do not understand, the CentOS Netinstall CD Installer does not contain a valid mirror list to select from, but asks you to type one yourself after choosing “Url” as location.
In Germany and for x64 just use http://mirror.netcologne.de/centos/6/os/x86_64/ (or something else from http://www.centos.org/modules/tinycontent/index.php?id=31
