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Apple's kernel is XNU. This is Open Sourced. Apple's GUI is proprietary code and is not Open sourced. However, the GUI is not the kernel.
So to be correct, Some of Apple's OS stack is open source, some of it is not. Specifically for this story, the kernel does not support Atom. The hackintosh community is going to "fix" the kernel to add support for Atom. Here's a link from the source itself. As a workaround, if you upgrade to 10.6.2, you can simply drop in the 10.6.1 kernel to fix the problem.
There is no "closed source kernel". You can find them at Apples Darwin site. As 10.6.2 has just been released, the corresponding XNU is not there, yet.
Your comment is full of fail.