So you do have Steam, did the Verify Cache that Wezqu wrote about and uninstalled and reinstalled the game like AndrewT said ( uninstalling the game from within Steam and manually deleted the CK2 directory in Mydocuments) ?
You need to tell us, we can't see what you are doing, what your PC is like etc. Every system is different. Its understandable your unhappy, but the probelm can't be resolved if all you do is rant.
Sounds as if you are on a 56kb modem or have quite bad internet connection. That's unfortunate and not as normal anymore nowadays, so nobody could know that for instance.
If you done all that, at least we know now that its probably not a corrupted download, while the error message you posted was suggesting this.
Disclaimer: I'm not a official guy here, just a forum member like most other.
I'll send you a Private Message.
(If you want to respond to the PM, please send a PM in return)