If you only need to reset a user's password, follow these instructions: Resetting your password is easy, but be sure to save your original system discs.
The following tips work for any Mac running Mac OS X 10.3 or later. Luckily, resetting a user or administrator password is pretty straightforward.
As an independent consultant this is one the more common issues I encounter. One of the most frustrating troubleshooting situations one may come across is when a user has forgotten his or her system password.