I would try bartPE. Microsoft doesn't support this so you will not find anything from them. You can find a lot of things for it, but mostly they are "Read" only bootable images. It is because there is a problem with USB<->OS during booting. Something about disablig USB, which basically kill booting. I tested a while a Vista booting from usb, which worked (not read only image). So try higher version of Windows, it could have been fixed...