I get an error that says something similar to "There was an error writing to your hard disk from battle.net, you may need to free up space." I just installed the game from battle.net, and the laptop I am using is brand new, and it most definately has enough space, so I am not sure what the main issue us.

Oh yeah, I forgot to mention that I am using vista 64bit, usually the root of all problems >.< Maybe its something else though

Run it in Administrative Mode.

I have this same problem, I just yesterday downloaded the frozen throne expansion online too, but how do I run the game in "administrative mode" ?

Oh I found out in a different thread, just right click the game and choose run as admin or something. It worked!