I have been playing with some Linux software called SPLAT! (http://www.qsl.net/kd2bd/splat.html). It is free software written by a ham to do RF propogation calculations and map coverage areas using free terrain data from the USGS. It does some neat stuff. I made some minor modifications and compiled it for Windows if anybody wants to try it out. You can find the Windows version on my blog at http://futuradio.blogspot.com/2007/09/rf-propagation-modeling-with-splat-for.html