Look closer at the example in the DBI documentation. Your connect() would probably work this way:

my $dbh = DBI->connect($dsn,$user,$password,
                       { RaiseError => 1, AutoCommit => 0 })
            || die "Database connection failed: $DBI::errstr";
[download]

The last argument is a hash reference. If you're not familiar with references, have a look at perlreftut and perlref. After that, maybe References quick reference.

Update: Also, since you're using RaiseError, you don't need to die explicitly. DBI will do that for you if there's a problem.