the wierd graphics you get only happen with ati cards the reason being its trying to use the built in apple drivers. These arent quite compatible. Boot into safe mode and install the right drivers for your card here are the ones i think are suitable.
http://forum.insanelymac.com/index.php?showtopic=107526

akso dont be suprised if you update osx and your graphix go odd again just reinstall the driver. If when you install it doesnt work upon reboot. Install using pacifist and tell it to replace with older versions as some installers wont replace with older files. You end up with a mix of part old and part new driver.


This should give you what you want

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