Ok guys!
Thanks for the help!!! I just figured out a solution (as i red the linked tutorial, it's kinda similar).
First i tried the analog cable. It has many resolutions including the 1280x800 i wanted, but the in windows the tray just dessapeard. Obviously the displayed picture is bigger than the monitor itself and as u cannot strecth, skew etc. the pic geometry on this type of monitor thats not a solution. so i pluged the dvi cable back in.
tried to add the custom resolution 1280x but the little error window just sad immediatelly that it could not be added. however i managed to add the 1024x640 to customs, set to it, tick the box "only show customs" and than pulled tha little bar from less to more, and bang, the 12800x800 just become avalible.
Thanx For the Help Again!!!
:bowdown