The best way to format a used hard drive is to place it into an external case or port and then connect it to the computer and format. Format a spare hard drive. See this article. To then connect the second hard drive you will need a space to put the hard drive...inside your computer case. A cable that has two connections coming off it.. If IDE then the second hard drive should be on the lower connection and the main hard drive on the top connection. The pins should be set to cable select. Here are a few more tips when putting a hdd in. You will need to know if you have a sata or ide drive so you have the right cable to connect. does any of this help?