"SQL Server and Windows NT" really means "You can use either SQL Server security or Windows NT security" or "both will work". So that is why you don't need to log into the NT domain if you use a username/password to log on to SQL Server.

As for the "opposite" server and login authentication, I haven't tried it but I would guess that a server in "NT security only" will prevent you from using any "SQL server security" logins you have created. And since "SQLServer and NT" allows both, you obviously won't get a problem using an NT authentication account.

Hope this clears thing up!

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>I'm a little confused about the security authentication "modes" in SQL Server 7 ...
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>Ok - you have either "SQL Server and Windows NT" or "Windows NT Only" set at the server level. This would seem to imply that "SQL Server Only" is not a choice - yet, we are able to log into SQL Servers without EVER logging into or having a password (or even an account) on/to the NT Domain. How is this possible???????
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>Now - there are also "Windows NT Authentication" and "SQL Server Authentication" choices on the login creation screen for the individual user. How do these properties interact with the server level properties? For example - what happens if you do Windows NT at the server level and "SQL Server" at the login level? or vice-versa?