As everyone, I downloaded the Windows 8 Developer Preview to start playing with what it looks like a big step forward from Microsoft.
I downloaded the Windows 7 USB/DVD Download tool to create a bootable USB pendrive and it failed with the error message “Unable to copy files…”
I used this very same pendrive to install Ubuntu, so I guess that, even though I formatted the disk, something was still there, on the boot sector or MBR.
I found the solution in this article:
Run "diskpart" from a command prompt with admin rights list disk select disk # (the number of your USB) clean create partition primary select partition 1 active format quick fs=fat32 assign
Run again the tool, it will work without problems now.