Ok I found last night another version of the video, 5+ mins long and with much bigger pictures than the first that I saw (which was just a little bigger than a thumbnail, without sound and lasting only 40-50 secs: the beheading in itself).
I have to admit that a lot of my questions are answered now (sorry for the disgusting details to follow): Nick Berg does move during the reading of his 'condemnation' (which he fortunately doesn't seem to understand). It's not a corps nor a doll. The blood is hard to see because the terrorists seem to have covered the ground with a dark brown mat, maybe to absorb the spilling. At some time I think it is possible to see the flow of blood.
And the time stamps are coherent with the hypothesis of 2 cameras recording simultaneously, the first with a 12:00:00 format time stamps, the second with a 24:00:00 format. One of the cams is 1 hour off, which is quite frequent with the daylight saving changes.
If I looked like an arnold to some of you, I'll accept it. It is only about me. However, I want you to know that my questions weren't meant to be disrespectful to the memory of Nick Berg but only a legitimate search for some truth during an era when images are potent weapons.
I'll also confess that, even after having been witness of some violent deaths or very serious accidents, I was much more upset by the second video than by the very first I saw. It suprised myself, because I knew what was going to happen, and what I was going to see, and I thought that I had learned over the years to rationalize such situations to avoid to be sucked into the emotional aspect of it. Bigger, clearer images, and sound were enough to shatter my resolve. I still don't assimilate Moslims with terrorists, and I'm still against the death penalty in most cases, but such a complete show of inhumanity only deserves the ultimate punishment.