Apple has said the Flat Panel iMac can only take PC133 RAM. Strange as it may seem the Apple System Profiler registers that RAM even when it is the correct kind as PC100. The only way on a Flat Panel iMac to detect whether or not PC133 RAM is installed is by booting from the included hardware test CD and running the hardware tests. That test CD will identify some errors if there are any. At one point I had some serious issues with a replacement motherboard that first wouldn't see my included RAM, and then the video went bad on it. The Hardware Test CD saw it as defective RAM at that time, but actually it was a defective motherboard.
