The MAIN Local Administrator account created when XP is installed cannot be deleted, however I believe the user account you are talking about is the User account you created for yourself, which is an Admin account by default. And there is also an account with Limited Settings.
The built-in Administrator account is hidden from Welcome Screen when a user account with Administrator privileges exists and enabled. In Windows XP Home Edition, you can login as built-in Administrator in Safe Mode only. For XP Professional, press CTRL + ALT + DEL twice at the Welcome Screen and input your Administrator password in the classic logon window that appears.
To have the Administrator account displayed in the Welcome Screen, try one of these methods:
Manual registry edit:
* Click Start, Run and type Regedit.exe
* Navigate to the following key:
HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ Winlogon \ SpecialAccounts \ UserList
* Use the File, Export option to backup the key
* Create a new DWORD Value named Administrator
* Double-click Administrator, and set 1 as its data
* Exit the Registry Editor.
And please check this aswell and see If anything help's, Microsoft Windows XP Home Edition:
The Administrator account is not displayed in User Accounts unless the computer is in Safe mode. To change the password for the Administrator account:
1. Click Start, click Turn Off Computer, and then click Restart.
2. After the computer completes the Power On Self Test (POST), press F8, and then click Safe mode.
NOTE: If you have difficulty getting to the Safe mode menu command, press F8 repeatedly after you turn on the computer.
3. Log on as an Administrator, or with another account that has Administrator permissions.
4. Click Start, click Settings, click Control Panel, and then click User Accounts.
5. Click the Administrator icon.
6. Click Create a Password or Change my password.
7. Type a password for the account, and then retype the password to confirm it.
8. Type a hint to help you remember the password in the event that you forget it.
9. Click Create Password or Change Password.