Install a third hard drive in a Dell Studio XPS...possible?

Does anyone know if I can install a third hard drive in my Dell Studio XPS computer. I am now trying to install a 3rd hard drive in the media bay right under the optical drive that came with the computer, but the screw holes do not align. Do I need a bracket to do this? Is it even possible or do I need to go with an external bay for the internal drive that I already have?

Thanks in advance for your help.