Currently Being ModeratedJan 12, 2013 3:29 PM (in response to Brie-Eating Surrender Monkey)
Your best bet is probably still going to be the Orbit behavior, with some modifications...
If you need a "3D-like" orientation, add a camera and set the project to 3D.
For each object:
Apply an Orbit behavior. Turn off the [Include] Y axis and turn on the [Include] Z axis. Adjust the Strength parameter to determine the speed of the orbiting object. (When you play this now, you should notice the size of the object changes in Z-space and that it will go behind the object it's orbiting around.)
Select the object and type Command - Shift - G to create a group containing that object. You can use the Transform Rotation X parameter of the Group to offset the "plane" of the orbit and use the Transform Rotation X parameter of the object with the opposite value to reorient the object vertically for the camera.
The orbits will now appear to be elliptical.
For the comet object, add a Basic Motion > Point At behavior and supply the car graphic. You might have to adjust the anchor point to give some extra distance from the comet's head to the car graphic, but properly set up, the tail should rotate through "space" and appear to point at the car object. If your comet is built of a circle and tail shapes in combination, then group those two objects and add the Orbit and Point At behaviors to that group. You will need to select that group and create another group to nest the comet graphic group as outlined above to adjust the "plane" and vertical alignment of the comet.
(Perspective view in the canvas -- a "car" object, a blue dot and a "comet" [grouped circle and "tail"] ... note the relationship of the "Anchor Point" which lies on the orbit behavior path and was adjusted to make the comet graphic appear to align with the orbit's center point)