Virtualization for free and runs on XP home edition too
Maybe you already knew this but VMWare now provides a free VMWare server package. It has most stuff that Microsoft VirtualServer has but you don't need Windows 200x and a VirtualServer license to just host some XP / Ubuntu images.
A nice thing too is that both Microsoft Virtual PC and Virtual Server don't run on Microsoft XP Home Edition and VMWare server runs just damn fine ;-) I need this at home because my new pc doesn't have installation cd's but only a recovery partition without installables.
Currently running Ubuntu and Windows 2003 and both run and perform quite well.