CentOS 5.8 was released today 8th of March.
You can download it from many mirrors, for example from FUNET: http://ftp.funet.fi/pub/Linux/INSTALL/Centos/
It installs just fine on an HP DL360 G7 with P410 and P411 controller.
CentOS has as far as I understand been slower at releasing updates than Scientific Linux (for example 6.2 was out 5 days earlier on SLC than on CentOS), this was not the case today though, SLC 5.8 is not available yet. Why?
Compare release dates here: