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Is it possible to remove the administrator's password on an XP machine?
There is no option/link in user settings as there is for standard users.

If you have the current password, it is easiest to login, change the password to blank and then logout.

If however you do not have the current password, but have administration over the machine,

1. Right click on My Computer.
2. Click on Manage.
3. Expand System Tools > Local Users and Groups > Users.
4. Right click on Administrator.
5. Click Set Password.

6. At the next screen, click Proceed.
7. Simply press OK, without typing a password.

This should work, so long as you do not have a complex or other password policy in place. If you do, and do not know how to remove it, please say and I will give you instructions.

Lastly, if you do not have local administrator access, I will probably question your intentions... but anyway, you will need a tool such as Offline NT Password & Registry Editor which will let you reset any password on the machine.

Of course, I need to say that setting a blank password really is not recommended, but I am guessing that you know what you are doing!