QUESTION:
Is there an interplanetary tracking program for missions such as MPF and
MGS, perhaps one that has an Orrery view?

ANSWER from Pieter Kallemeyn on August 19, 1997:
The best method for tracking the postions of interplantary probes is to
obtain astronomy software that'll allow you to input the orbital parameters
of comets and asteroids, and use those "slots" for spacecraft orbits. 
Obtain the orbital parameters of the probes from their respective web sites
(Pathfinder's web site is http://wwwmpf.jpl.nasa.gov) and you're set.  This
is precisely what I do to obtain a quick plot of the various spacecraft
about the solar system.

Pieter Kallemeyn, MPF NAV team chief