Hello I am trying to install Ubuntu 12.04 on my early 2009 imac following these instructions http://lifehacker.com/5934942/how-t...-and-take-back-your-powerhouse-apple-hardware After I reboot my computer with rEFIt installed and the Ubuntu dvd inside, I get to the point where I can choose between "Install Ubuntu" or "Try it from the disc". The problem is that no matter which option I choose a black screen appears and after some time the disc stops spinning and nothing happens. The black screen has two purple colored vertical lines of pixels (both about an inch long) on the top left corner of the screen. I think the problem may be the GPU because my computer in some occasions freezes, (usually, but not always, when playing games) and sometimes green and violet lines of pixels appear on the screen when that happens. Is there any way I can install Ubuntu on my computer? Any help is greatly appreciated!