Avoid the urge to proselytize. There is virtually zero chance that you'll be able to convince a bunch of C++ programmers that Perl is better than anything in less than 10 minutes. To this end, don't attempt to explain how easy, flexible, or DWIMish Perl is. Show how to accomplish some task, but let the audience make their own value judgments. gjb is onto something good with the suggestion to show how DBI provides code portability over various DB backends.
Keep your presentation directly related to the themes you're working on in the class. This will help ensure that your classmates are on the same page as you during your presentation, and make your instructor happier when assigning a grade.
If you give code samples, you're probably better off expressing concepts using pseudo-code. Even explaining the most basic elements of Perl like scalars and arrays will needlessly eat up your time. So, distill the core ideas and express them in a language-independent way.