Mon 21-Apr-08 01:05 PM | edited Mon 21-Apr-08 01:47 PM by R Owen
The two modes are similar but different. The mirror lockup is for sensor cleaning and maintenance, and reducing vibration on slow shutter speeds/long focal lengths. To use ML you would compose your photo place the camera in ML mode then trip the shutter.
Live view does lock the mirror in the up position and allow you to use the back panel LCD as a view finder, or a PC if you have the camera control software installed. By watching the monitor you can compose your photo then trip the shutter either with the camera/a remote/or remote software.
This is most likely a very simplified explanation but that is how I understand it an how I use it. Hopefully someone else can add the technical details.