To change the login to the standard logon box, go to "Control Panel" -> "User Accounts" -> "Change the way users log on or off" and uncheck "Use the welcome screen for fast and easy logon". It should be reflected in this registry key.
Note it is possible to momentarily change the Welcome Screen to the standard logon screen, by holding down the keys CTRL and ALT while pressing DEL twice. This can be useful if needing to login with a "hidden" account not shown on the Welcome Screen. In WinXP Pro it can used to login with the builtin Administrator account.
[HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \Windows NT \CurrentVersion \Winlogon]
LogonType = 0 (Classic = 0, Welcome Screen = 1, Default = 1)
More Info MS KB291559
Note when the Welcome Screen is enabled and Require CTRL + ALT + DEL at logon is disabled (DisableCAD), then it is not possible to lock the computer again using CTRL+ALT+DEL, but it will instead start Task Manager. More Info MS KB281980
Note it is possible to configure what users should be presented on the Welcome Screen. By standard all but special system accounts are displayed on the Welcome Screen. One can hide an account from the welcome screen or force a hidden system account to appear by adding a DWORD registry key with the username:
Related Configure Automatic Logon
[HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \Windows NT \CurrentVersion \Winlogon \SpecialAccounts \UserList]
Administrator = 1 (Visible = 1, Hidden =0)
More Info MS KB827072
Note in WinXP Home one can only access the builtin Administrator account if booting into safemode. By default the builtin Administrator account has no password.
Note in WinXP Pro the Administrator account is only shown on the Welcome Screen, if no other account is part of the Administrator-Group. One can still login using the account if holding down CTRL+ALT and pressing DEL twice.
Note in WinXP an account is only shown on the Welcome Screen, if it belongs to either of these groups Administrators, Power Users, or Users.
Related Advanced User Management in Windows XP Home
Related Appearence of the login and welcome screen in WinXP
More Info MS KB279783