Thank you for the explanation, especially the link was helpful, Noah!
I also want to thank Martin for his support and effort in writing SOAP::WSDL.
I have set now the include dir by using:

PerlRequire /XXX/example/startup.pl

I have one more question (possibly again with an easy answer):
How is it possible to get a valid response when browsing for my web service, from the browser?
I ask because since I moved to Mod_Perl2, I just get:

Length Required

A request of the requested method GET requires a valid Content-length.

instead of the default page showing the methods.

Thanks again,
Andreas