It turns out that Microsoft has acted more proactively than even tz database or World Time Explorer, in setting up a page for the San Luis inhabitants that by now will wake up Monday morning to a new schedule, one hour behind the rest of the country. The page about how to change Windows operating systems to accomodate the San Luis change, however they don't specify a new timezone, instead the rather more relaxed solution to go back to either the timezones "(GMT-3) Buenos Aires, Georgetown" or the intermediate timezone "(GMT-3) Georgetown" which both represents GMT-3 without DST implementation all year round: http://www.microsoft.com/argentina/dst/sanluis.aspx The below page recommends how to change the Argentina DST timezone properly to have the start and end times for the Argentina-country-wide change effectuated the 30.th. of December 2007: http://www.microsoft.com/argentina/dst/actualizacion.aspx At the time of writing it is Sunday 2007-01-20 22:35 CST -0600 and so it should be Monday 2007-01-21 02:35 ADT -0200 in most of Argentina and Monday 2007-01-21 1:35 SLST -0300 in the San Luis province. (I invented SLST for San Luis Standard Time, it is certainly not an official abbreviation!) Are there any news "on the ground" in San Luis that the change is going ahead? I'll take action tomorrow for WTE if this is the case. Regards, - Jesper Jesper Nørgaard Welen Email: jnorgard@Prodigy.Net.mx Project Leader (Líder de Proyecto) Software CIMMYT - Centro Internacional de Mejoramiento de Maíz y Trigo Dirección: CIMMYT Int. c/o Jesper Nørgaard Km. 45, Carretera México-Veracruz El Batán Texcoco, Edo. de México CP 56130 MEXICO Tel.: +52 (55) 58-04-20-04 ext. 1374 Fax: +52 (55) 58-04-75-58 Tel. Casa: 53-10-05-95 ó 53-10-97-78 Download the shareware program World Time Explorer, I made: http://www.worldtimeexplorer.com/index.html