I was trying to create a bootable USB with Windows 8 using the “Windows 7 USB/DVD download tool”. It kept failing with a message that it was unable to copy the files. (I was using a 16gb USB stick).
After some searching, I found that if you make the USB stick bootable manually, then you can use the tool and it copies all the files successfully.
Here are the steps:
Open a command prompt window in administrator mode.
Run the following commands
diskpart list disk select disk #
(Here replace # with the disk number. Be careful to select the correct disk number, else you may end up loosing all your data).
clean create partition primary select partition 1 active format quick fs=fat32 assign exit
Now re-run the “Windows 7 USB/DVD download tool” and you should be able to successfully create a Windows 8 installation USB stick.