Problem is solved!!!!!
It appears that not all ICH8 sata connection are idential at al!!!!
When I plugged the Sata with OS not in the next slot number after the Sata DVD-rewriter but in the adjacent bank I coul boot up and find the Sate in the BIOS indicated as Master.
Now I have the Sata with OS in the original sata slot 1 back again and the second Sata in the bank with higher slot number and in BIOS I will see it as the fourth master.
This peculiarity is fortunately nowhere to find in the P965 user guide.....