How to run OS on USB disk

How to install and run a FULL Windows XP from a USB drive 12 Apr 2008
http://www.ngine.de/article/id/8

Running VMware ESXi Hypervisor
http://blog.torh.net/2009/02/22/running-vmware-esxi-hypervisor/

实战：在USB设备上安装VMWARE ESXI
http://www.vmbest.com/school/13-vmware-esx-school/111-actual-combat-the-usb-device-to-install-vmware-esxi
How to Run Chrome OS From A USB Drive
http://www.pcworld.com/article/183136/how_to_run_chrome_os_from_a_usb_drive.html

Seven steps to a bootable Windows 7 thumb drive
http://www.crunchgear.com/2009/01/21/seven-steps-to-a-bootable-windows-7-thumb-drive/

 How To Install Windows 7 On USB Flash Drive
http://www.intowindows.com/install-windows-7-on-usb/