http://www.gamewinners.com/playstation/GranTurismo.htm

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http://www.gamespot.com/ps2/driving/granturismo4/hints.html

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http://www.absolute-playstation.com/api_tips/tgranturismo2.htm

http://www.cheatcc.com/psx/codes/gt2.html

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http://www.cheatcc.com/psx2/gt4.html