If your user account has no password, or if the password has 8 or more characters and was originally created in Mac OS X 10.2.8 or earlier, you could be unable to log in after installing Leopard. To prevent this problem, follow these steps:

1. Open the Accounts pane of System Preferences.

2. Select your account in the list on the left.

3. If the lock icon in the lower left corner of the window is locked, click it and enter your password to unlock it.

4. Click Change Password. Then:

• If you previously had no password, leave the Old Password field blank; enter and verify a new password, and click Change Password.
• If you have a password with 8 or more characters, and you think you might have created it in Mac OS X 10.2.8 or earlier, enter your old password, enter and verify a new password with 7 or fewer characters, and click Change Password.

You can change your password back to what it was previously, after upgrading to Leopard. (This information was taken from Take Control of Upgrading to Leopard.)

—Posted by Tonya Engst on February 19, 2008