One of the big problems that the wind indusrty has run into in developing wind farms is that people do not want to see the towers. You can use some very expensive software to do a viewshed analysis, but I have found a very afforable alternative. Global Mapper has a built in function to be able to download elevation data from the web and then with a simple puch of a button to run the analysis. You can customize the variables for the tower height and even look at the terrain in 3D. I use have the expensive software (I am sure you know which one I mean) and it is not this easy to perform a line of sight. Global Mapper also has many other great features and the ability to work with a huge variety of file formats, mainly ESRI shapefiles, KML, and Mr. SID imagery. If you think that Global Mapper could be useful, you can download it free to try it.