CentOS is an enterprise Linux distribution made using Red Hat Enterprise Linux packages. CentOS 5.3 is a slight update.
Installation went flawlessly on VirtualBox. Boot time was very long (about 2 minutes). Once booted, the system was very responsive and used only 130 megabytes of RAM.
This distribution uses outdated software (2.6.18, GNOME 2.1, OOO 2.3, etc...), so there is no reason to choose it, even for mission-critical computing. Take a look at Ubuntu 8.04 or SUSE Enterprise 11.
Here's the video demonstration: