I read this excellent article on setting up Holidays:
http://docs.opengroupware.org/Members/sasepp/sasepp/view?searchterm=holidays


I am using OGo on a Debian Sarge server, paths vary according to distribution and install method.


Partial content of
/usr/lib/opengroupware.org-1.1/webui/OGoSchedulerViews.lso/Resources/Defaults.plist

// holidays
scheduler_show_holiday_shrovetide = NO; // Fastnacht
scheduler_show_holiday_ascension = NO; // Christi Himmelfahrt
scheduler_show_holiday_mothersDay = YES; // Muttertag
scheduler_show_holiday_corpusChristi = NO; // Fronleichnam
scheduler_show_holiday_summertimeChange = YES; // Sommerzeitumstellung
scheduler_show_holiday_wintertimeChange = YES; // Winterzeitumstellung
scheduler_show_holiday_christmasEve = NO; // Weihnachtsabend
scheduler_show_holiday_newYearsEve = NO; // Silvester
scheduler_show_holiday_deathsSunday = NO; // Totensonntag
scheduler_show_holiday_newYear = NO;
scheduler_show_holiday_holyThreeKings = NO;
scheduler_show_holiday_goodFriday = NO;
scheduler_show_holiday_easter = NO;
scheduler_show_holiday_firstMay = NO;
scheduler_show_holiday_whitsun = NO;
scheduler_show_holiday_germanUnityDay = NO;
scheduler_show_holiday_reformationsDay = NO;
scheduler_show_holiday_allSaintsDay = NO;
scheduler_show_holiday_christmasDay = NO;
scheduler_show_holiday_boxingDay = NO;
scheduler_show_holiday_firstAdvent = NO;
scheduler_show_holiday_secondAdvent = NO;
scheduler_show_holiday_thirdAdvent = NO;
scheduler_show_holiday_fourthAdvent = NO;
scheduler_show_holiday_dayOfPrayerAndRepetance = NO;


scheduler_show_holiday_holidaygroup_bay = NO; // Bayern
scheduler_show_holiday_holidaygroup_ber = NO; // Berlin
scheduler_show_holiday_holidaygroup_bra = NO; // Brandenburg
scheduler_show_holiday_holidaygroup_bre = NO; // Bremen
scheduler_show_holiday_holidaygroup_bwb = NO; // Baden-Wuertt.
scheduler_show_holiday_holidaygroup_hes = NO; // Hessen
scheduler_show_holiday_holidaygroup_hh = NO; // Hamburg
scheduler_show_holiday_holidaygroup_mvp = NO; // Meck.-P.
scheduler_show_holiday_holidaygroup_nrw = NO; // Nordrein-W.
scheduler_show_holiday_holidaygroup_nsa = NO; // Niedersachsen
scheduler_show_holiday_holidaygroup_rpf = NO; // Rheinland-Pf.
scheduler_show_holiday_holidaygroup_saa = NO; // Saarland
scheduler_show_holiday_holidaygroup_sac = NO; // Sachsen
scheduler_show_holiday_holidaygroup_sah = NO; // Sachsen-Anhalt
scheduler_show_holiday_holidaygroup_thu = NO; // Thueringen
scheduler_show_holiday_holidaygroup_slh = NO; // Schleswig H.
scheduler_show_holiday_holidaygroup_bylaw = NO; // Gesetzl. Feiert.
scheduler_show_holiday_holidaygroup_advent = NO; // Advent

scheduler_show_holiday_holidaygroup_custom_all = YES;
scheduler_show_holiday_holidaygroup_custom_private = YES;
scheduler_show_holiday_holidaygroup_dk_feriedage = YES;



-------------------------------------------------


Content of my /var/lib/opengroupware.org/.libFoundation/Defaults/Holidays.plist file

{
scheduler_everyyear_holidays = {
"dk_feriedage" = {
"01-01" = "dk_nytaarsdag";
"06-05" = "dk_grundlovsdag";
"12-24" = "dk_juleaftensdag";
"12-25" = "dk_juledag";
"12-26" = "dk_juledag2";
};


"custom_all" = {
"02-02" = "dk_kyndelmisse";
"02-05" = "dk_mary";
"03-08" = "dk_kkampdag";
"04-01" = "dk_reden";
"04-09" = "dk_besat";
"04-16" = "dk_margrethe";
"05-05" = "dk_frit";
"05-26" = "dk_frederik";
"06-05" = "dk_farsdag";
"06-07" = "dk_joachim";
"06-11" = "dk_henrik";
"06-15" = "dk_genforening";
"11-10" = "dk_mortensaften";
"12-13" = "dk_luciadag";

};
};


scheduler_2007_holidays = {
"dk_feriedage" = {
"04-01" = "dk_palmesoendag";
"04-05" = "dk_skartorsdag";
"04-06" = "dk_langfredag";
"04-08" = "dk_paaskedag";
"04-09" = "dk_anden_paaskedag";
"05-04" = "dk_store_bededag";
"05-17" = "dk_kr_himmelfartsdag";
"05-27" = "dk_pinsedag";
"05-28" = "dk_pinsedag2";
};
};

scheduler_2008_holidays = {
"dk_feriedage" = {
"03-16" = "dk_palmesoendag";
"03-20" = "dk_skartorsdag";
"03-21" = "dk_langfredag";
"03-23" = "dk_paaskedag";
"03-24" = "dk_anden_paaskedag";
"04-18" = "dk_store_bededag";
"05-01" = "dk_kr_himmelfartsdag";
"05-11" = "dk_pinsedag";
"05-12" = "dk_pinsedag2";
};
};
}



--------------------------------------------

Localized strings
------------------

Partial content of:
/usr/share/opengroupware.org-1.1/translations/Danish.lproj/LSWScheduler.strings

holidaygroup_dk_feriedage = "DK feriedage";



Partial content of:
/usr/share/opengroupware.org-1.1/translations/Danish.lproj/OGoSchedulerViews.strings

dk_skartorsdag_dk_feriedage = "Skærtorsdag";
dk_langfredag_dk_feriedage = "Langfredag";
dk_paaskedag_dk_feriedage = "Påskedag";
dk_anden_paaskedag_dk_feriedage = "2. påskedag";
dk_store_bededag_dk_feriedage = "Store Bededag";
dk_kr_himmelfartsdag_dk_feriedage = "Kristi Himmelfartsdag";
dk_pinsedag_dk_feriedage = "Pinsedag";
dk_pinsedag2_dk_feriedage = "2. pinsedag";
dk_palmesoendag_dk_feriedage = "Palme søndag";
dk_grundlovsdag = "Grundlovsdag";
dkjuleaftensdag = "Juleaftensdag";
dk_juledag = "1. Juledag";
dk_juledag2 = "2. Juledag";
dk_nytaarsdag = "Nytårsdag";
dk_farsdag = "Fars dag";
dk_kyndelmisse = "Kyndelmisse";
dk_luciadag = "Luciadag";
dk_kkampdag = "Kvindernes Intl. kampdag";
dk_mortensaften = "Mortens aften";
dk_besat = "Danmark besat 1940";
dk_frit = "Danmarks befrielse 1945";
dk_genforening = "Danmark genforenet 1920";
dk_reden = "Slaget på Reden 1801";
dk_mary = "Kronprinsesse Mary";
dk_margrethe = "Hendes Majestæt Dronningen";
dk_frederik = "Hans Kgl. Højhed Kronprins Frederik";
dk_joachim = "Hans Kgl. Højhed Prins Joachim";
dk_henrik = "Hans Kgl. Højhed Prins Henrik";