The following question may be trivial, however, I just can't make it clear to
myself, even after reading through the Books Online.

I have two machines in the same network.
A hosts Sql Server (named AS), B access the database ASD in Sql Server AS.
A has windows logon info as UserA and PasswordA, (administrator account).
B has windows logon info as UserB and PasswordB. Application is running
under this account.

The Sql Server is set to Windows and Sql Serevr Mixed Authentication Mode,
The database ASD has a UserAS and PasswordAS as the db owner.

My question is:To successfully access AS from B, does the connection first
pass A's window authentication, then pass the AS's SQL Server authentication
(if set to Mixed Mode)?

If this is true,
What connection string (in ADO.Net) should I have to connect to the Database?
Or, what authentication settings I should have(set) to make a successful
connection in the case describled above (B access AS on A)?

I observered, with the following string to work: "user
id=UserAS;password=PasswordASD; data source=AS;initial catalog=ASD; persist
security info=True;" , I should first set the A's login credential in B by
visiting B's network place.

Additional Question:
When I use Windows NT Integrated Security from B, which username and
password is used to acess AS on A?

When I use specific user name and password, how to create a pair of username
and password in AS so that the username and password can be authenticated by
the windows A and sql server AS.

Thanks.