Quite a few people have written in asking when their country will start selling tickets, I will have to look into it further, but I do think it depends on the country and perhaps even the local theatre owners.
Jerm writes: just got report from the biggest Belgian Movie complex (Kinepolis) that one can start buying his/her tickets starting from December the 17th.
Jan writes: In Germany the Ticket Sale for FOTR starts officially on Thursday 22nd. The date is even mentioned at the end of the "new" LotR-Trailer. On a side-note: This is the FIRST movie to officially start on a WEDNESDAY in Germany. The official release day for movies over here is normally on a Thursday. One can only thank Warner Bros & New Line for this wise and very cool decision.