Here's a mediocre trailer for the new season on YouTube. According to the Wikipedia article on Lost, it looks like there are at least eight finished episodes "in the can" for Season 4 out of sixteen episodes anticipated. The writers' strike may have an impact on when the second half of the series airs.
Also of note in the Wikipedia article, the following regarding future seasons/episodes:
"In May 2007 it was announced that Lost will continue for its fourth, fifth, and sixth seasons, concluding with the 117th produced episode in May 2010. These three final seasons will consist of 16 episodes each, running weekly in the spring uninterrupted by repeats."
I can't remember being as excited about a television series as I have been with Lost. If you haven't succumbed to its siren song, there's still time to catch up on DVD before Februrary!