I installed Railroads! using Paulthetall's instructions (setting the game to run in a window and disabling the intro movies is not necessary, as it turned out) and by and large, the game runs well and smooth on my 13" MacBook Pro (Nvidia 9400M, 4 GB RAM, MacOS X 10.6.3 and CXG 8.1.4) with the settings on a medium level.
But: the game crashes after roughly 10 minutes, every time.