The username and password of a user with full access and privileges to the database in question. Mostly, the username and password of the user who creted the database. By database I don't mean MSSQL Server (the database server), but something like "ClientsDatabase" or whatever.
Of course, in a Windows world there may be no username and password. I am not sure if MSSQL Server will allow that. In that case I suppose an empty string would do.
Hope this helps.