Well... a bit disappointed no one could answer. Here is the result of my further investigation.
I have 'solved' the problem by removing the dual display setup into single display.
So: only one display: MCE runs fine. I can choose LCD or TV, both work in single display mode.
Dual (copy) display generates the freeze.
Ergo conclusio: a combination of W7, MCE, Nvidia 96.85 vista whql driver, Nvidia FX5500, who knows may tell me..
I am filing this issue under hardware compatibility.
I have to live with 'either' display, which, for this time, I can, even when I cannot always see the characters on the TV screen.
If I have to admin my PC I am using Remote Desktop through my laptop and WiFi.