AFAIK the most OpenGL implementations render the points as squares. Actually on the gf8800 gtx it was the first time I have seen round points. If you want this behaviour on all cards I would suggest to use billboards with a texture.
Thnx. I’ll check for the alpha blending, but I’m sure I disabled anti aliasing.
Furthermore it turns out that under Linux (ubuntu) problems do not occurs. Only the Windows driver seems to render squares. I hope it is not a matter of driver implementation?
As NiCo suggested, it could be that in Linux you’ve enabled antialiasing in the NVIDIA control panel (nvidia-settings) which is overriding your application’s settings.