Red Hat

It shares some of the same issues as xen in that it has limited support for guest oses. It does not support netware and as far as I am aware offers nothing in regards to management. We need to set-up 20 or so virtual machines in a rather complex san infrastructure.

Unfortunately virtualbox at present seems to be aimed at the desktop. I use it intensely for virtualizing windows on my laptops and it does a wonderful job but I couldnt imagine using it to manage a whole infrastructure .

Marius

Running Xen without the proprietary paravirtualization drivers is disappointing. Look at VMware or Virtual Iron. VMware Server is free, so you can use it if you like.
Virtual Iron, however supports very little. Even on the Linux frame it is very dependent on some things, and can only work if you have hardware assisted virtualization at the CPU level, such as AMD's Pacifica or Intel's Vanderpool.

Not entirely. Vmware ESX used a 7.3 redhat kernel for part of its processing, and some of the userspace but it is really a stretch to say "Vmware is Red Hat," because that's the kernel it boots, and not the hypervisor or associated drivers.