The easyest way would be to log into your machine as root. You won't even have to bother using Terminal though. But you will encounter one problem - root has its own password that is hidden to you. But there is a nice workaround.
Step 1:
Go to applications/utilities and open NetInfo Manager. A window will appear.
Step 2:
You then select users/yourname.
Step 3:
Click on the lock at the bottomn of the window and enter your administrator password (you have to be logged in as an administrator at this time). Now NetInfo Manager is unlocked.
Step 4:
In the lower list choose the value for passwd, highlight and copy it in the clipboard.
Step 5:
As before, go to users/root in the upper list in the window. Select it.
Step 6:
In the lower list choose the value for passwd, highlight and paste from the clipboard.
Lock again. That's it. Root will have you password now, which you can use in the log-in process. (Log out first!!!)
What it does?
Root got another password than you selected while installing OSX for the administrator. I think, Apple wanted to make sure, all the Mac Users that like moving things around in the system, cannot make severe damage to the system. In OS9 you could damage your machine seriously, but OS10 is off for another horizon. It's Unix. So if you are not sure about how it works - better don't explore your new possibilities by trial and error. Remember, logging in as root gives you total control over the system. It's powerful stuff - and you have been warned.
Nevertheless, I think we should decide on our own whether to log in as Donald Duck, Administrator or even root. We're grown up people here. This is why I showed you the trick.
Your password is scrambled in NetInfo Manager. But if you copy the scrambled password to root's password - the system will believe it`s the same password.
Later,
Roman
Still, I am not sure if it works from OSX.