In the extension ARB_Point_Parameter, there is a reference to POINT_FADE_THRESHOLD_SIZE_ARB, which is supposed to provide transparency when the computed point size is smaller than the provided treshold. The specs of the extension seems pretty contraditory though about multisampling, smoothing and fading. Anyhow, I never got the treshold to work. Anybody ever tried it with succes?
Well I guess the question was too hard... Was it? ;-)