Atari has just announced that they will now be offering the 7 day free trial to European customers starting today (April 5, 2004)! Here is the official word from their site:
Game Network in cooperation with Atari would like to announce that starting from next Monday, 5th April a 7-days trial version of Horizons: Empire of Istaria will be available for the european players. More details about how to apply to the trial and where to download the client will be unveiled during the next few days.
We expect they will be posting more details anytime now at their site (http://www.europe.istaria.com)