I stumbled on some links today that allude to a mysterious thing called X#.  At one time you could Google X# and get some results, but now all references to X# have vanished.  If you have the X# demo video I would love to see it.  Here are some links I know of (Thanks Roy!):

http://zerotrilogy.gotdns.com/jaysonblog/archive/2003/12/13/171.aspx

Xen and X#: One and the Same

Microsoft 'X#' On Tap?

Microsoft Research Looks to Extend C#

Microsoft Expands .Net With Xen

Microsoft's Box Riffs on Life Inside The Empire

Xen is it the new name for X# ?