How to create a complete recovery Image for my new netbook

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http://askubuntu.com – I just got a new acer netbook, it comes with windows 7. I wanted to know how I could create a recovery image using tools like dd. I want to know what command creates the exact backup of the hard disk and how I could restore it incase things go wrong when I try to install linux. I have an external hard disk on which I will store this image and a bootable usb drive with ubuntu 12.04. If this isn't the best way then do suggest alternatives. (HowTos)