ActivePerl is not part of Windows XP. However, it is possible that it is used on the server that you are browsing. The "intrusion" is not originating from you. The mechanism is an exploit of a weakness in earlier versions of ActivePerl; the site is trying it on you for whatever reason.
What is Perl? Perl (Practical Extraction and Report Language) is a programming language, originally from the Unix world, designed for text handling and now available for many platforms. It's now a very powerful language and something of a cult among its fans.