Change a Windows XP Password

You must be able to log onto the Windows XP machine as an administrator before you can change any passwords.

Steps

Log onto the computer as an administrator.
Click on Start, then depending on your setup, either click on Control Panel or move the cursor to Settings and then click Control Panel.
Once Control Panel opens, either click or double click User Accounts, once again depending on your setup.
In the User Accounts dialog box, select the user account who's password you want to change and click the Reset Password button.
Type the new password in the Reset Password dialog box and confirm the new password and click OK.
You are done. You can now log onto the computer with the other username and new password.

You can also do this on windows 98. On Windows 98, you do not have to log in as an administrator.

If you are trying to change the currently logged in user's password, just press Alt-Ctrl-Del, choose Change Password and then enter in the existing and new passwords into the provided dialog box.
You cannot change the password without knowing it in all computers.
Denying someone access to property or information to which they have a right can be illegal.