So I'm doing some tinkering with Darwin again as I'm trying to get kqemu to work on Mac OS X. I don't think it will work but since I'm motivated I'm using this as an excuse to learn. :-)I've just downloaded the kernel sources, the extra kernel tools, and XCode 2.4 from Apple's sources. Actually I'm still downloading the XCode sources, big stuff (940MB)! While I have a little experience with kernel modules from my times with Gentoo and debian, I'm new to them on OSX. Thankfully, Amit Singh and the MacFUSE project have provided a little bit of details for kernel extensions on OSX.
And the Kernel Extension Overview from Apple.com. Over my head.