Resetting Mac OS X Passwords

I've just had to do a bit of Googling to help out a colleague who was trying to reset a forgotten password on a PowerBook, and figured this might come in useful later:

• Reboot in single user mode by pressing Command+S
• Type /sbin/fsck -y if you want to run a filesystem check
• Type /sbin/mount -wu / to mount the root partition
• Type /sbin/SystemStarter to start NetInfo and the usual system services
• Use nidump passwd . to get the list of users
• Change the password in the usual fashion (passwd user) etc. and reboot

Don't forget that only the first "normal" user has administrative privileges by default.

• Press Option (or is it Option-Command-O-F?) for OpenFirmware, useful to eject cd forcefully and mac-boot afterwards.
• Press Command-Option-P-R to Reset Parameter RAM (PRAM) and non-volatile RAM (NVRAM)
• Press X during startup to force Mac OS X startup
• Press Option-Command-Shift-Delete during startup to bypass primary startup volume and seek a different startup volume (such as a CD or external disk)
• Press C during startup to start up from a CD that has a system folder
• Press D during startup to start up from the internal HD
• Press N during startup to NetBoot
• Press R during startup to force PowerBook screen reset
• Press T during startup to start up in Firewire Target Disk mode
• Press Shift during startup for Safe Boot mode (temporarily disable login items and non-essential kernel extension files)
• Press Command-V during startup for text boot (Verbose mode)
• Press Command-S during startup for single-user mode
• Press the mouse button to eject the CD

More here and here.