Dual boot Windows8 + Ubuntu 12.04.2 gone wrong

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http://www.linuxquestions.org – Bought a new box with Windows 8 pre-installed (64 Bit). What I tried to achieve: Setting up dual-boot for Ubuntu 12.04.2 and the existing Windows - both as EFI boot. I have successfully resized the big data partition from within Windows to make space for Ubuntu. The problem when starting the installation: the Ubuntu installer claims there is no other OS present, which is worrying as it might destroy Windows if I proceed. Normally, I remember, they give you the option "Install Ubuntu alongside with Windows", or soemthing like that. So, I didn't go on installing Ubuntu but tried to (HowTos)