Well that's disappointing. I thought I'd try the free trial to see if it was available from the unmetered steam server on my new wireless connection (8GB a month only, but I'm finally in a broadband world). But I can't get any of the little tools people have made to block steam from other content servers on wine so I have to use my only late windows machine which only has 10 GB free and I find despite the steam store page saying it needs
Hard Drive: 8 GB free hard drive space
Steam wants 15189MB! Another wonderfully accurate store page and I see the Civ IV page still suggests it works on win 2k!