I'm in the process of getting root access to my new phone. I followed the steps at http://unlockbootloader.sonymobile.com/instructions, but I got stuck at step 13. Windows would not accept the android_winusb.inf file I downloaded from Sony.
I used USBView to find out if the Vendor ID and Product ID fit to the numbers in the inf file, but did not find a problem there. Then I noticed that while all the other entries are present in both
[Google.NTx86] and [Google.NTamd64] sections, "; SonyEricsson" is missing in the latter. And the OS is actually the 64 bit version ...
After copying the %SingleAdbInterface%, %CompositeAdbInterface%, %SingleBootLoaderInterface% entries under [Google.NTamd64] Windows finally accepted the driver.
Just a side note to step 15, the fastboot.exe is located under 'platform-tools', not 'tools'.
One step closer to bricking the phone!