Excuse me for the long absence.
I have finaly overcome some more difficulties to make a clean install of Windows 7, farewell Vista.
In the process a had more hassle with other drivers, so I think this issue here was caused by (at least for me) irrepairable drivers. The last advice of creating a bat file was beyond my scope and since succes was at least doubtful, I took this radical step.
Getting Arduino IDE to run with the new OS was a matter of 5 minutes.
Thank you ballscrewbob for your help.