If you mean can you load a 64-bit version of Windows on a USB and boot
your computer from that, the easy answer is no. The short answer is the
USB port gets reset while Windows is still loading from the USB flash.
On the other hand, if you mean can you install a 64-bit version of
Windows on a USB that can be used to install Windows onto a hard drive,
then the answer is yes. I believe the Windows 7 USB/DVD download tool
will reformat the flash as part of the ISO transfer but I'm not 100%
certain on that.
More on the Window-7-usb tool can be found at this rather long URL,
among others that a Google search will turn up.
http://www.mydigitallife.info/windo...d-disc-or-usb-flashhard-drive-from-iso-image/