Starry Night can read satellite orbital elements directly from a two-line-element file. The North American Aerospace Defense Command (NORAD) defined the TLE format as a way of succinctly describing a satellite's orbit in a small number of characters. NASA and the Goddard Space Filight Centre make available the TLEs for many current satellites.
Starry Night looks for a TLE file called Satellites.txt in its SkyData folder when it starts up and, if found, will load the positions of the first 150 satellites found in this file (in Enthusiast and Digital Download only 10 satellites are loaded). Since the orbital elements of satellites are constantly changing it is a good idea to update this Satellites.txt file from time to time.
To download, right click (or click and hold on Macs) and, depending on which web browser you are using, pick "Save This Link As...", "Download Link to Disk", or "Save Target As...". After downloading, move Satellites.txt to your Sky Data folder, replacing the older copy.
Alternatively you can download the TLE text file directly from Orbitessera website. This website also has a lot of good information on the structure of two line elements with some history and explanations. The TLE file found at the Orbitessera website is updated frequently, often once a day, so it is a good way to get the most recent satellite elements. Note however that you will need to change the name of the downloaded TLE file from the Orbitessera website to "Satellites.txt", place the file into the Sky Data folder and restart Starry Night before the new orbital elements are updated.
If you are tracking a specific satellite that you want to add to Starry Night try using the Orbit Editor. The Orbit Editor is a good tool for learning about celestial mechanics. Celestial mechanics is usually passed over in introductory Astronomy courses, because the mathematics and time needed to grasp orbital concepts is just too involved for most students. Starry Night provides an interactive simulator where the orbital elements of an object can be changed in a visual manner making a complex subject understandable and, dare we say it, fun.
For more information about adding a new planet, asteroid, satellite, moon, or comet to Starry Night see "Using the Orbit Editor".
This page tracks the 100 brightest satellites and gives their NASA two line elements (TLE).
Iridium bills itself as the worlds first handheld global satellite telephone and paging network. The satellites that were put into orbit for this network can be tracked using the TLEs found on this page. More Iridium info.
A good collection of weather, navigation, military, and communications satellite elements from the Celestrack website.