you really should go with a [link|http://www.cse.iitk.ac.in/~amit/courses/371/abhishe/main.html| Sterling Engine ] rather than steam. Live steam is fairly dangerous and the Sterling was developed in part to answer those dangers.
Of course, Sterlings (like Steam Engines) do suffer from some problems. They're not instanteous (they have to heat up first), and they don't have the power curve that gasoline engines have.
However, during the 1970's, Ford and other manufacturers did look at the [link|http://abcnews.go.com/sections/scitech/CuttingEdge/cuttingedge011130.html| sterling engines. ]
[link|http://www.motorshow.or.jp/eng/show/history/history_23.html| Note the Nissan ]