I want to use my external HD (MyBook) for my Time Machine Backup but when I went to back it up it told me that the MyBook was not formatted for it. I used this HD to transfer pictures and documents from my old PC computer to my Mac and it transferred correctly. I did notice that for some reason when it is plugged into my Mac, there isn't an option to create a folder in the MyBook. I wanted to put all my other docs in separate folder as to only have 2 folders on my HD...the backup one and the docs one but it won't let me do it in my mac...it will let me do it if I reconnect it to my PC.