Welcome to PT, datsuns2002.
In answer to you question: That depends on where you live and the policies of your local theatre. Here we can only buy tickets up to one week ahead.
Last year, the official Newline LOTR site (www.lordoftherings.net) had a link to ticket purchasing for ppl in USA. They may again as the release date gets closer. Have you checked with you local theatre? Large theatres, such as Empire Theaters, have web sites which may be helpful.
anyway, I hope you enjoy exploring all the nooks and crannies of Planet-Tolkien.