This is the latest value rackmount offering from Dell. It's a great spec for the price, but installation of CentOS 5 seems surprisingly difficult, thanks to the SATA DVD drive used in the unit. RHEL/CentOS doesn't have the driver for the controller so can't find the DVD during installation. I'm sure there are other workarounds (network install, USB DVD drive etc.), but eventually I got hold of a Redhat driver disk from Dell Support (it doesn't seem to be on the Dell site btw).
I've uploaded the disk image here; just uncompress it and copy the .img file onto a USB key. At the installation command-prompt type 'linux dd' and then hit Enter. You'll then be asked for the location of the driver disk image; just navigate to the USB disk, select the image, and you're in business.