Hi Stuart,

For comets: use Extras... Add MPC Comets/Asteroids, and click on
"Click to download updated comet data and add it to Guide."

For asteroids: I'd recommend that you make use of MPCORB. This is
described at

http://www.projectpluto.com/mpcorb.htm

For a long time, Guide has had a fixed, burned-onto-the CD set of
asteroid orbital elements. It's a rather elaborate system, and allows
for speed and accuracy over a long time span. But the rate at which
asteroid data changes (new objects found, new observations made causing
updates to existing orbital elements, new numbering/naming of objects)
is making that almost impossible to support. So use of MPCORB
definitely appears to be the way to go.

-- Bill