To register the game on the forums, use the Steam key (if you purchased it through the indie gala/bundle).
If you only get a 690MB file, try removing local content for the game by right clicking it in the steam library. Then delete any files related to KA2 from your user/steam folders manually. Then restart Steam and reinstall. Please let me know how that works out.
If you only get a 690MB file, try removing local content for the game by right clicking it in the steam library. Then delete any files related to KA2 from your user/steam folders manually. Then restart Steam and reinstall. Please let me know how that works out.