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 untick Use the Welcome Screen
5 click Apply Options

You will now be able to log on to Windows XP as Administrator in Normal Mode