Unfortunately when you hide a user account in Vista or Windows 7, it is no longer available at log on or Switch User. It's basically the same as disabling the user account.
An alternative is to unhide the user account, and use the log on with user name and password
option along with the CTRL+ALT+DEL
secure log on screen. This way none of the user account's names are displayed, and you have to know the user name and password to log on to a user account.