It's actually 440, but 512 won't hurt in this case. You copy those bytes from the boot disk that you careated through the CentOS process, right?? Then you copied them to the file boot.lnx on C:, right? Still, I doubt this will work because your drive is on USB, and the USB disks are not mapped to device names until later in the boot process. Note: I've never tried booting off USB before.