The administrator account does not appear by default. If you need it (assuming you are using XP Pro)at the Welcome screen pres ctr-alt-del twice. The log on screen will appear and you can type the administrator in the user name box and then the password.
To set it up to use permanently (not a good idea if you have other users) open a command prompt and type
lusrmgr.msc This will open local users and groups.
In the console tree click Groups. Double click the Administrators group and remove all accounts except Admin. Open the Users or Power users groups and click Add to replace each of the users you removed.
This is only possible with XP Pro.