Everywhere you turn, everyone is touting "Virtualization". It's in magazines (This month's Linux Journal), its all over the web (Xen) and even on TV with the IBM commercals (the one with trying to contain a growing number of servers).

Xensource is a company steup to help support it. 

if you don't know already, Xen allows you to use one machine running Linux and Xen to provide support for multiple guest operating systems instances/virtually running on top of the main operating system.