Generally by default, Windows XP displays the user name of the last user
who has logged successfully in the system. However you can make the User
name box in the Log On to Windows dialog box as blank by editing the value
entry of HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Logon
as 1. For further detailed instructions, please access the URL given below:
Note: The information is given below is Non-Microsoft information, but it
may help you resolve the issue.