The Perl/C interface has undergone change at various stages. The Dynaloader your code references was used for Perl v 5.004 for dynamically loading C libraries. From Perl v5.4.5 XSLoader now does this job, although I am not sure what the official forward/backward compatibility status is. See XS and XSLoader for more details.

Update: The Dynaloader is ongoing it seems, but see Dynaloader, for the latest documentation, given that a lot has changed since v5.004 when Dynaloader first came out.