From the DBD::Pg documentations section on the connect method:

"The following connect statement shows almost all possible parameters:"

$dbh = DBI->connect("dbi:Pg:dbname=$dbname;host=$host;port=$port;optio
+ns=$options",
    $username,
    $password,
    {AutoCommit => 0, RaiseError => 1, PrintError => 0}
    );   );
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So try:

my$dbh = DBI->connect("DBI:Pg:dbname=five;port=5432", 
'postgres',
'',
{ RaiseError => 1, AutoCommit => 0 }) or die "kon de database niet ope
+nen!";
[download]

Update: Changed wording of the opening sentence.

Update 2: Added blank password, thanks erix

Hope this helps

Martin