Having just shortly written an iCal calendar client in perl/Tk to replace Sunbird, I can show you the iCal related module-list I use:

use Date::ICal;
use iCal::Parser ();
use Time::Local;
use Date::Calc qw( Mktime );
use Encode qw( encode );
use Data::ICal::Entry::Event;
[download]

Note the Date::ICal wich is not Data::ICal.