I'm a little confused about the security authentication "modes" in SQL Server 7 ...

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???????

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?

TIA!