I'm torn about this. I consider the Dark Tower King's best work, and up there in my favorite books of all time (it's a series I literally have been reading since high school). However, movies from books don't translate well, case in point, Bourne Identity (a fine movie, but incrediably cut down from the original book), 99% of Stephen King's other movies, and a host of others. See my previous comments on this.
The only way to do the DT justice is to make it a mini-series, with a minimum 8 hours per-book.
I can only pray that this doesn't destroy my memories of this series :)