http://www.kernelthread.com/mac/osx/arch_startup.html

At end of startup sequence (but before the graphics startup), /etc/rc
runs /sbin/Systemstarter, which runs stuff out of 
/System/Library/StartupItems and /Library/StartupItems.

"SystemStarter -n -D start|stop|restart SERVICE" lists debug and dependency 
info.
N.b. SERVICE is something listed in "Provides" in the 
StartupParameters.plist file.

http://cfm.gs.washington.edu/secureity/firewall/osx-10.1-ipfw/

http://www.macdevcenter.com/pub/a/mac/2003/10/21/startup.html

SystemStarter obsolete?
http://developer.apple.com/documentation/macosx/Conceptual/BPSystemStartup/Concepts/BootProcess.html#//apple_ref/doc/uid/20002130/CJBBICAB


SystemStarters use vars set in /etc/hostconfig