The Mac OS X Startup Apps List
A number of keyboard shortcuts are available for you to change the way in which your Apple Mac OS X device works. These should all be pressed after the boot chime, before the grey Apple logo appears on your monitor.
C – with this, you can opt to boot from CD or DVD rather than the computer’s hard disk.
T – this is a great option, one that allows you to start up your Mac in “FireWire target mode". This means that your Mac is now an oversized Firewire storage device!
X – use this to boot into Mac OS X if you have a computer that dual-boots into OS 9
N – to start your Mac from a network drive, press N as the computer boots
SHIFT – possibly one of the most common maintenance start-up options, pressing SHIFT boots your Mac into safe mode
Mouse button – clicking the mouse button after the chime ejects any disc in your Mac’s CD or DVD player before booting.
OPTION key – situated between CTRL and COMMAND, the Option key can be pressed at boot to allow you to choose a start-up disk.