he meant the brightness you can set in the game, press start in driving mode to open the menu and then display -> and set brightness to 0.
works fine with GSDX9, but you get a blackscreen after ~5 seconds.
i'll try it with ZeroGS when i created the ISO, i booted it directly from GameDVD before and that was slow.
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My System: C2D E6700 @3.4ghz | Asus P5W DH Deluxe | 4GB DDR2 800 | eVGA Geforce GTX 260 55nm SC-Edition
Tutorial: Hardware Antialiasing in PCSX2 (DX9 only)