Most people have a very insecure installation of Windows XP. They have no administrator password… This account only appears in the list if you boot into safe mode by pressing F8 as the machine is starting up. It is an easy way to access someone’s PC and look at their files. However secure your password on your own account, an administrator can take ownership of your files in order to view them.
To add an administrator password, log into safe mode, go to control panel, user accounts, all make sure all administrator accounts have passwords. This includes the Administrator account itself as well as any others with administrator status.