For Lion or Mountain Lion
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
When the menubar appears select Terminal from the Utilities menu. Enter resetpassword at the prompt and press RETURN. Follow instructions in the dialog window that will appear.
- Start up from your Mac OS X Install DVD.
- From the Utilities menu, choose Reset Password....
- Reset the password for the affected account(s).
I am running 10.6.8
Model Name: Mac Pro
Model Identifier: MacPro5,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 2.8 GHz
Number Of Processors: 1
Total Number Of Cores: 4
L2 Cache (per core): 256 KB
L3 Cache: 8 MB
Memory: 12 GB
Processor Interconnect Speed: 4.8 GT/s
Boot ROM Version: MP51.007F.B03
SMC Version (system): 1.39f11
SMC Version (processor tray): 1.39f11