Sony Vaio HD Replacement help

Hi. Need to replace HD on a Vaio VGN-AR61M. All the video instructions I found on net showed different models. These require pulling off the bottom and the keyboard and top panel. But my unit seems to have simple access after removing the HD cover panel on the bottom. There is even a empty space for a second HD.
Am I missing something or can I just pull the HD case out and replace the HD and reinstall? Is there anything I need to do to get the Vaio to recognize the new HD. I plan to install Ubantu/Linux(new kernel) without WINDOWS.
I need detailed info since I am not an experenced tech. I live in a remote area and am the only person in area with any PC repair experence at all so this job fell to me. My experence:confused is mainly as a sound engineer converting lunchboxes into portable HD recorders back in early 90's.
THX