In your link below it seams that my problem can not be solved :-( It is written that Winwos 7 does not support scanning via network but only supports direct connected all-in-one machine to my laptop.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=1140784&prodTypeId=18972&prodSeriesId=1140784&objectID=c03056313
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=1140784&prodTypeId=18972&prodSeriesId=1140784&objectID=c03056313