usb flash drive - Transfer a working Windows XP installation to USB pen

I would like to put my working windows xp installation on a usb pen and get rid of the hard disk (it's a video poker machine so performance of usb is not an issue and hd break very easily).
How can I achieve a perfect and bootable copy from my hd to my pendrive?

Thanks a lot!

Answer

See Clone\Restore your installed XP to usb-hd, including comments.