Enable Administrator in Welcome Screen

When you install Windows XP an Administrator Account is created (you are asked to supply an administrator password), but the "Welcome Screen" does not give you the option to log on as Administrator unless you boot up in Safe Mode.
First you must ensure that the Administrator Account is enabled:

1. Open Control Panel
2. Open Administrative Tools

3. Open Local Security Policy
4. Expand Local Policies
5. Click on Security Options

6. Ensure that Accounts: Administrator account status is enabled.

Then follow the instructions from the "Win2000 Logon Screen Tweak" ie;
1.Open Control Panel
2. Open User Accounts
3. Click Change the way users log on or log off
4. Un-tick Use the Welcome Screen
5. Click Apply Options
You will now be able to log on to Windows XP as Administrator in Normal Mode.

Another Method

By default windows XP doesn't show the Administrator in the user list at the welcome screen. Here's a way to get around it.

Now head up to HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\CurrentVersion\

Winlogon\SpecialAccounts\Userlist

create a new DWORD entry and name it as Administrator and change its value to 1.

exit and reboot for the changes to take effect.
To change it back change its value to 0 or simply delete the key.