http://www.maximumpc.com/files/u57670/gtx570_iso_med.jpg
those two notches where the bracket makes a 90 degree corner, you screw down into the case slots. Those 2 holes on the bracket that you have highlighted aren't for anything.
you can see what i mean if that doesn't really make much sense
http://pc.mmgn.com/lib/Images/contents/P3070046.JPG
the screw is just supposed to hold down the card, not fasten it in.
Er okay wait just to clarify, look at the very top metal bracket part of the card ( on left side of the card ) you see how theres 1 squarish hole in the center and 2 semi open holes at the very edge. You are saying to slip screws into these 2? So far I've been slipping a zip tie into the center squarish hole and tying them tightly around the case bracket holes to hold it down.