use DBI;
my $dbh=DBI->connect("dbi:mysql:hostname=localhost;database=somedb","userok","passwdok");
bless $dbh, "My::Special::DBI::db";

print "can error: ", $dbh->can("error"),"\n";

package My::Special::DBI::db;
use base qw(DBI::db);

sub error {
   my $dbh=shift;
   return $dbh->errstr();
}

##</code><code>##

perl -v
This is perl, v5.8.7 built for x86_64-linux-gnu-thread-multi

perl -v
This is perl, v5.10.0 built for i486-linux-gnu-thread-multi