Back in the good old days of 1.x, you could draw a line, then draw an object, and make the object move along whatever line that was. It was great.
Then the lovely redesign of Impress came, and that user-defined motion path feature got lost along the way. It was a sad time.
However, now in 2.3 it's back! It works slightly differently, but it's great. In addition, you can edit the existing motion paths like the stars, etc. Here's how it works.
Draw an object, then under Custom Animation’s Motion Paths tab, select any one of the first three effects.
cursor will change so that it will draw the kind of line you
selected. Draw the path that you want the object to follow. Then run
the presentation to see the effect.
To edit existing motion paths, just apply a standard motion path like Eight-Point Star or Diamond. The path will appear in the slide. Click on the path and expand it; you’ll get another path (there’ll be two diamonds, for instance). Delete the old path, and you’re good.