Here's the process I have undergone:
-Created a BattleNet account and entered the Key Code
-Agreed to the installer's ToS (or whatever it exactly is)
-Wait less than twenty seconds and receive the error:
"ERROR: Unable to initialize streaming. Please heck your Internet connection. If this problem persists, please contact Blizzard Technical Support. (InitializeStreaming)"
I have no idea what else I can do other than wait and see if it is just a problem with so many people trying to do the same thing as I.