I had to re-install the Debian bootloader after installing Windows 7 Ultimate and I did this by loading up my OpenSuse x64 installation DVD and selecting the rescue option which gave me a login prompt. I logged in as root and after following the Gentoo chroot guide to set up a chroot to my Debian installation I could then type grub-install /dev/sda that re-installed the proper grub bootloader to the hard disk MBR. The Debian installation DVD would have been useful for this, but I did not have that to hand. The video I have embedded shows how to do this with super grub CD, but the chroot option will work fine. If the installed operating system is 64 Bit then the live CD has to be also. I have Windows 7 Ultimate installed on one hard disk and Debian on another and I press F12 to select which hard disk to boot from. That is why the Gigabyte H55 motherboard is so good.