I recently acquired an IMac G3. This unit has the previous owner's login information in place, however, they do not know their password, nor is there a system disk available. Is there any workaround to be able to access this computer?
There are two parts to this, if you have access to the terminal prompt on another user, skip step 1.
Step 1
Single-User Mode
Another interesting modification to the startup process is booting into single-user mode. Holding down Command+S will start Mac OS X in single-user mode, allowing an administrator to directly access the system through a command-line interface. This is a last-resort method of booting your computer that should be used only if absolutely necessary.
Single-user mode boots in a text-only fashion, just like the verbose startup mode. The process finishes by dropping the user to a shell:
Caution
Be aware that the single-user mode command prompt carries with it full root access. This is not a place for playing games or learning Unix.