If you still have problems, maybe try it step-by-step; first remove any ATI kexts from /S/L/E to be able to boot properly and delete /System/Library/Caches/com.apple.kext.caches
Next install an inject (something that tells OS X where and how it has to find & use a device) that uses a framebuffer you think will gonna give you a working display, this can for example be the bootloader with GraphicsEnabler like in my tutorial, ATY_Init.kext by netkas (check Info.plist for used framebuffer) or a modification of the DSDT.
Then check for your inject to work - for example those booters I have compiled will report as "ATI Radeon HD 4650" in System-Profiler, where also the injected Framebuffer (Motmot, Shrike or Flicker) should be displayed (PCI-Cards section).
Once you are sure the inject works add the Framebuffer driver (ATIFramebuffer, ATI4600Controller & ATISupport) - be sure to have your device id in ATI4600Controller and that those three ones have the same version (must not be the one that belongs to your OS X build).
Once you have working display and resolution change add X2000 with your device id in it. Use only X2000 matching your OS X version / frameworks!! and see if it will give you graphic accerlation.

In case of doubt try all three booters with any connection to the display possible with your equipment - even stupid combinitions like HDMI & DVI2HDMI at the same time...

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