The problem with your question is that fully functional depends on what functionality you want. If you're writing Web scripts in Perl, you'll need a Web server; if you're writing mail server plugins, you'll need a mail server; if you're writing database applications, you'll need a database. Perl is a general purpose programming language, so "fully functional" covers a lot of ground. You'll have to be much more specific about what you'd like to do if you want a full answer, but hopefully the other answers will provide a good start.

Good luck!