how to access Administrator after adding a new user

If so, from the welcome screen you can press Ctrl-Alt-Del and bring up the classic login option. From there you can type in the username and PW of any defined account. If you want the administrator account available with the welcome screen, I'll suggest you download the MS powertoy "tweakui". You can use it to add or remove users from the welcome screen including the administrator account.

because you apparently just renamed the original default admin account.

These are the steps to hide a user account so simply follow the same steps but after locating the account in the key set the value to 1 (ONE to show) rather than 0 (ZERO to hide)

The user accounts you've set up appear on the Welcome screen (another new feature in Windows XP) when you start up the PC. To hide one of the user accounts so that it doesn't appear here, go to:

# HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList

Right-click anywhere within the Registry Window and click New to create a new DWORD value with the name of the account to be hidden. Set the value to 0 (decimal). This account won't be accessible when switching users with Fast User Switching; you'll only be able to access it from the Log On To Windows dialog box. Keep in mind that it is not a totally hidden account; the account's profile will appear in the Documents And Settings folder. Also, the account appears in Local Users And Groups when an administrator is logged on.