Screaming Penguin - Source Does Matter

Both RedHat and SuSE made efforts last year to get Xen into the Linux kernel. And kernel maintainers said it would happen soon (last year). I am not sure if that has occurred yet, but either way it soon will be easier to utilize xen via Linux as major distros have announced planes to incorporate it.

RedHat says RHES 5 will have it and SuSE says 10 will have it as well.

Fedora Core 5 will have it next month.

And Xen has been in the unstable Fedora tree for a year or so now.

For more on Xen LinuxJournal has a few nice articles:
Introduction to the Xen Virtual Machine
Virtualization in Xen 3.0.