It's entirely free. You need ActivePerl, the Windows Scripting Host ((WSH) comes per default with XP), optionally the Windows Script Component Wizard and the Windows Script 5.6 Documentation.

In a nutshell you create so called .wsc files, that contain code and metainformation so that script code can act as a COM component. the script code can be written in any language the supports the WSH, including Active Perl.

Please see the "PerlScript", "Perlscript Examples" pages of the ActivePerl docs and the examples at \Perl\eg\Windows Script Components.