Reset code location?

["Jayson Smith" <ihatespamratguynospamplease@insightbb.spamsucks.com>]

Here's a silly question. Where is the code on an Apple that runs the instant 
you hit Reset or switch the power on. Or is there some special code not 
anywhere in accessible ROM or something? In other words, if a program wanted 
to trigger the series of events that goes with hitting Reset, E.G. beep, 
check the power-on byte, go through the reset vector if valid, otherwise 
scan for a disk controller and boot, could it do it, and how would it go 
about doing this?
Thanks.