I wanted to try playing online, so I went there, and it of course asked me to install the patch. This is the second time I've tried this (having gotten this error in the process before), so I knew where to look.
I followed this thread's instructions (downloading the first link, second link, and downloading DirectX 9.0c all by itself), and now have an error I don't think has been mentioned. It tells me, when I try to load Civilization (Vanilla, BTW), that d3dx9_32.dll is not a valid Windows image.
Any help?