Yes I have tried the "winusb.dll", including following the instruction from PICO's site.
I also have tried different computer-systems, including Windows 7 and older computer-device & OS.
So far, all of them are not OK and giving the same responds: ". . . Unknown USB-Device, etc. . . ."
Yesterday I went to the Supermarket and bought for Euro 1,-- a general purpose USB-printer cable,
and see there, wow, all computer-systems start to recognise those two devices as "PICO USB-Dive, etc., etc....".
I think those two supplied white USB-cable should be the cause for the mentioned problem.
It seems these two cable just simply terminate the Plug-&-Play function of the PICO's USB-Oscilloscope devices.
What is so special inside these two white USB-cable in respect to the simple general purpose one ?
At last, everything is worked fine for me, even without any special installation-steps.
Just use the latest software downloaded form the PICO's site.
I also have found out that the latest software could always be installed
on older computer-device without latest Windows Update,
however using an older software-version, it was possible to do the installation and made everything work.
Anyhow, thanks for all your support. I think we can close this topic, at least speaking for myself.