I still have the flicker, with ATI HD2400. It's 100% OpenGL related, because i tried it on 3dsmax. If i choose the DirectX viewport driver it works without problems, but when i switch back to the OpenGL mode it starts flickering again. Another thing is that it flickers only if the viewport is refreshed. Since normally 3dsmax is divided into 4, only the area which covers the refreshing viewport will flicker.