The blog Winter is Coming which is following the HBO treatment of George R. R. Martin’s fantasy novel A Game of Thrones is reporting that the script for the pilot episode has been leaked. Looking at the few first pages of the PDF it looks to be closely based on the first few chapters of the novel.
An earlier post includes a review:
The first episode remains faithful to the source material, but not stubbornly so. Scenes exist in the script that don't take place in the book. Some of this is for convenience--there's only sixty minutes to cram in all the details we need. Other changes take advantage of the visual medium that is television. Lots of dialogue and internal thoughts are omitted in favor of knowing looks and sidelong glances. It's subtle, but effective.
The goal is to turn each of the five or more published and unpublished novels in the series into one year’s worth of television episodes.