try to use Macbook graphics driver then i think it will solve out...

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AMD Rocks You'r feature--


AMD Phenom II X4 955 @3.2GHz
Gigabyte MA770T-UD3P
MSI Nvidia Geforce 9600GT
4GB DDR3 RAM
Western Digital 500GB, Western Digital 320GB HardDisk
Samsung SyncMaster 24" HD & HDMI LCD Monitor
Microsoft Wireless Kit
Mini USB Bluetooth 2.0
Mini USB Wireless Adapter 2.0
POWERLOGIC ModenaGTX2000 (Modified Mac Casing)