pretty hard to work out what you are doing from non functioning code, note the following requires the SetGraphicsDriver defaultFlags to be set to 0 for single buffering to work correctly (and adding a flip doesn't seem to affect output):
SetGraphicsDriver GLGraphicsDriver(),0 Graphics 640,480 glClear GL_COLOR_BUFFER_BIT GLDrawText "'Raw' OpenGL Graphics! Hit any key...",0,0 glflush WaitKey