Glad you asked – cuz io9.Com has the answer:
by Charlie Jane Anders
You might already know that Game of Thrones filmed a pilot that never aired. With different actors playing Daenerys and Catelyn, and a few other changes. Not much is known about this earlier Thrones pilot, except for a few hints — but a copy of the script was posted online. Here’s all the scoop about the Westeros you never saw.