Screen flickering and computer freeze
You can see posterize effect on backgroung when screen is flickering:
http://flic.kr/p/9qPfzB
MacPro2008, Mac OS X (10.5.8), 2x3Ghz, 4GB800Mhz RAM, NVIDIA GeForce 8800 GT
MacPro2008, Mac OS X (10.5.8), 2x3Ghz, 4GB800Mhz RAM, NVIDIA GeForce 8800 GT
Has a fix on page 28 for those with ATI cards.
Screen flickering and computer freeze