As for the Perl flavour i can strongly suggest Strawberry Perl? You'll get a perl installation with a lot other useful packages preintalled and cpan and cpanp client working out of the box having a C compiler bundled.
As far as i know, concerning free memory, you can release memory to the pool used by that Perl process, no to the operating system.
L*
There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
On ActivePerl, cpan works out of the box without having a C compiler bundled. You also have the option of downloading prebuilt binaries, so it gives you more options than Strawberry Perl.
I would strongly suggest using Linux or Unix. You can EASILY install a virtual server on your Windows machine and be up and running with a full featured Perl distro in an environment that is much more conducive to open source programming. Welcome to the 21st Century.