I have never been a fan of auto logon instead of security but on virtual machines protected by a front end password it seems to make sense.

To Activate auto logon on Windows XP after enabling multiple accounts use regedt32 to navigate the registry to the key
HKEY_LOCAL_MACHINE\SOFTWARE\MicrosoftWindows\CurrentVersion\Winlogon
Set or create the string keys
DefaultUserName to the desired user name
Set or create the DWORD key
AutoAdminLogon to the value 1