I found this question and it is very similar to my situation. I am satisfied with zkriesse's answer but I want to know whether data in my external hard disk would be lost using this method. And what about Fernhill Linux Project's method ?
Also, I downloaded the Universal USB Installer and thought of directly installing Ubuntu to drive J: (which is my external hard disk) but for that, I had to check "Now Showing All Drives (BE CAREFUL)". Would anything go wrong if I go ahead ? Why does it say, "BE CAREFUL". Would anything go wrong if I install ubuntu into drive J: directly without checking the "Format J:\ Drive (Erases Content)" checkbox ? I repeat that I CANNOT AFFORD TO LOSE A SINGLE BYTE OF MY DATA IN THE EXTERNAL HARD DISK.