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You can also use google, as these are very common problems.
Install netloader from the windows rescue mode.
... take care: Windows often tries to erase any linux it sees.
Install grub from the Ubuntu live desktop CD.
Open a root terminal and enter "fdisk -l" and make a note of which /dev your external drive is. The internal drive will be /dev/sda ... so it's the other one. Lets say /dev/sdf.
Then enter "grub-install /dev/hdf".