So OSX is junk, we all know that 
What do you do with a nice quad-Xeon Xserve? Install Linux and use it as a Xen host. Sounds easy, but it’s not. I’ve not managed to get it to work yet, but here’s what I’ve gotten to work so far.
The Xserve uses EFI as a BIOS replacement. It does not have BIOS emulation that the desktop & laptop Apple models have. As such you need a Linux kernel with EFI support. To cut a long story short, there is no EFI support in x86_64. However, there should be in a few days time
http://lkml.org/lkml/2007/8/13/604
We’ve gotten EFI to load a kernel. The kernel then hangs after loading and expanding the initrd. I think this is because it makes a BIOS call that does not exist. In order to get a kernel to load, ignore the optical drive. The easiest way is to get a fat formatted USB disk, copy a vmlinuz kernel and associated initrd onto it. Then run elilo to install the EFI version of lilo onto the USB disk. You’ll then have to tweak the elilo.conf file on the USB disk to point to the correct kernel and initrd.
I’ll update this “guide” in a few days, when we’ve (hopefully) gotten Debian installed.