Why do my tables not show up if I leave my connection on the default database?

While I was setting up an ODBC connection in Windows 7 via the Administrative Tools, I noticed that if I don't check "change the default database to" during the setup in the ne开发者_运维技巧xt step after putting in the user ID and password for the connecting DB, the list of tables are not what I should be getting.

More specifically, during the "Microsoft SQL Server DSN Configuration" setup process is where the "change default data base to" option appears.

1. What does this do?
2. what is the point of picking "master" (selected as default)? It looks like I need to actually choose the name of the DB that I'm connecting to.
3. I wasn't able to perform INSERT-queries. I found an article for a solution here, however, if I'm writing the queries in PHP, how do I execute the ADO code MyConnection.Execute "SET ARITHABORT ON?