Hi Martin,

One can use the Extras... Add MPC Comets/Asteroids function.
Do this, and click on "click to download updated comet data
and add it to Guide." This will cause Guide to download the
current comet info from the Minor Planet Center, and to merge
it with its existing data. (The merge is needed because MPC
doesn't provide a complete comet database, just one giving some
data for current objects. A complete comet database would be
very handy -- the merging process can cause headaches -- but as
far as I know, no such animal is publicly available.)

-- Bill