To aid in setting up for one of these events - a wonderful program is available on the web called CalSky. The software predicts transits of the ISS against the Sun and Moon for any given location on Earth.
To see how well this worked I used CalSky to find a transit that happened near my house on July 10th 2010 at 14:30:54.5 MST. The weather was marginal with thunderstorms building all around and the local seeing was very turbulant. As a test of the predictive accuracy of CalSky I setup my Questar 3.5" and my Canon 5D MKII in video mode to see if I could capture (at least to the first order) one of these events.
I postioned my setup in the parking lot of a local business which was supposed to be on the centerline of the transit path. The clouds impaired my view somewhat - the Sun being washed out by a rapidly moving layers of cumulonimbus avil haze during the 0.4 seconds it took for the space station to move across the face of the Sun. Below is a map of the path where I setup and the final image which is a sum of 14 video frames from the 5D HD movie. It is obvious that the Space Station did not cross the center of the disk as predicted but I consider the test successful enough to move on the the next step - getting an individual full resolution image of the ISS in transit.
