This shouldn't be stopping you from playing, or is it just too visually jarring?
Anyway, you can download a non-steam version of the game from one of our mirrors:
http://www.arcengames.com/aiwar_buy.phpYou can just install that (and the updates that pop up in game), and play that. Your steam license keys will work for it.
Alternatively, you could take the graphics out of that install and copy them to your steam version.
We're working on getting the proper graphics into the next steam update; they were in the files we sent up last time (iirc) but I think there was just some confusion about them being needed, etc. Everyone's ridiculously busy over there.