When calculating comet positions it's important to use up-to-date orbital elements. Not only are new comets constantly being discovered, but orbital elements for comets slowly change with time, and can only be used reliably for a few weeks.
The organization responsible for coordinating new comet discoveries and producing authoritative orbital elements is the Central Bureau for Astronomical Telegrams. They kindly make these element sets available in a format directly suitable for use by a number of different astronomy programs, including SkyMap and SkyMap Pro. To download the latest element set and prepare it for use by SkyMap or SkyMap Pro, proceed as follows:
Note that if you are using SkyMap Pro 10 or later and are connected to the Internet, you can use the Tools/Download Data menu item within SkyMap to download up-to-date comet data at any time.
NB: The download link for comet orbital elements has changed since the program was released. If you get an error trying to download orbital elements from the program, select the "File/Preferences/Downloaded Data" menu item, and set the URL for downloading comet data to:
When you next run SkyMap, the new orbital elements will be available for use. Note that you will have to use the Options/Comets...menu item to select the comets you wish to display on the map.
Some historic orbital elements are available here.