I have good news and bad news now :-)
The good news is that after searching at PerlMonks again and studying e.g. Adding modules to a PC manually
and ActiveState Module Install Without PPM
and after that http://docs.activestate.com/activeperl/5.12/faq/ActivePerl-faq2.html#ppmx_files
- since there are ppd- and ppmx-files - I was able at last to install extra modules in my ActivePerl distribution at work without administrator authority and without communication with the IT department.
This is really good news since this extends my options in programming (and - first of all - learning) Perl.
Now the bad news. I installed Chart::Gnuplot and faced the same problems which were already described at Chart::Gnuplot and Windows XP. Since my script runs ok now - thanks to you guys - I am going to keep using / developing it at least by now.