MAKE Magazine‘s (see yesterday’s entry) blog pointed me to the Tom’s Hardware article Windows in Your Pocket, which describes how to create a bootable Windows USB drive. With a valid Windows XP setup disk, some free utilities, and a fair amount of fiddling around, you can create an emergency boot device to be used for rescue, virus scanning, disk partition backup, and many other things.
I don’t know if it’s possible to use the thing to boot a computer other than the one on which you created it. I suspect not, due to the Windows XP activation system. Even if possible it’s likely a violation of the license agreement.