I've finally fixed the problem. It was neither "Alternate Pixel Center" nor "Support DXT texture format", but I found it in the same guide, so thanks anyway. the solution is on page 9 in the guide. you must use Rage3D Tweak to disable "Tile backbuffer", "tile primary buffer", "tile textures" and "texture micro tiling". more information is on page 9 in the guide (http://www.tweakguides.com/ATICAT_9.html
Thanks everyone who has helped me from the beginning of this thread. I can now finally buy the game (I have borrowed the game from a friend this far) and play it without errors.