Live preview is not an option... on a DSLR the mirror is down and the Sensor is not constantly on to deliver live-feedback (opposite to a P&S).
What can be done however is to use nikon capture camera control ... that is a little addon for capture & Capture NX which allows so called Tethered Shooting...
basically you link the camera to the computer switch it on and control it from the computer.
works well... but you actually have to take a shot to see the results.
I use this a lot when I do table-top studio photography, where the camera is mounted to a sturdy tripod and I can directly take, save & review the shots on my notebooks monitor instead of the cameras "tiny" LCD (D70s, not really "tiny" but nothing compared to a 15" )
The mirror lock-up fuction on the D80 is only used for cleaning the CCD. Otherwise, the mirror is only up during the time the CCD is being exposed to the light coming through the lens.
I don't think that the CCD is energized during mirror lock-up.