Running Windows Vista and XP In Ubuntu With Multiple Desktops!

I am considering installing VirtualBox either in Windows or in Ubuntu and run the other as a virtual machine. While surfing the net, I came across this YouTube video. This video shows someone running and flipping through Windows Vista and Windows XP in Ubuntu Linux with multiple desktops. One desktop contains Ubuntu's own desktop, while one has VirtualBox running XP and another running Vista:

VirtualBox is an open source virtual machine software that allows users to run multiple operating systems inside an existing operating system. Errr... you get the drift?