FWIW, the DBD::Driver and the database-server-docs usually contain details for constructing a DSN :) Hope this helps
SQL Server 2008 Connection String Samples - ConnectionStrings.com
Server=myServerAddress;Database=myDataBase;User ID=myUsername;Password
+=myPassword;Trusted_Connection=False;
Data Source=myServerAddress;Initial Catalog=myDataBase;Integrated Secu
+rity=SSPI;
http://search.cpan.org/dist/DBD-ODBC/FAQ
my $DSN = 'driver={SQL Server};Server=server_name;database=database_na
+me;uid=user;pwd=password;';
my $dbh = DBI->connect("dbi:ODBC:$DSN") or die "$DBI::errstr\n";