So I've been thinking how cool it'd be to make my sims jump off a cliff
I made the animation using MS3D and this tutorial :
http://www.youtube.com/watch?v=7dfk6rN4IUY
But as I press the start button my sims move into a horizontal position, never descending to the ground
I tried moving the auskel joint along with my sim but nothing changed
Thoughts ?

Don't touch the auskel joint, it's supposed to stay in place (don't rotate, don't move).

If you want to rotate the whole sim, use the "root_rot" joint. If you want to move the sim, use the "root_trans" joint.

Make sure to not move the "root_rot" joint or rotate the "root_trans" joint, or you'll mess up the animation, and make sure to select them from the list, because they overlap.

If you've done anything with the auskel joint, or done the wrong transformations with the root joints, you usually have to start over, because that's easier than fixing it (at least in Milkshape - not sure if it is possible to fix it in Milkshape).

Thanks for the helpful information!
So I assume there is no way to make sims fall to the ground from a high distance using MS3D?
If not, is there any other program you can do this with?

Like I said, you have to use the "root_trans" joint to move the sim. This joint moves the whole skeleton.
If you want to rotate the whole skeleton, you have to use the "root_rot" joint.

Don't get these two mixed up.

Don't do anything to the auskel joint (no moving or rotating).

A different posebox tutorial with some more tips on what to do and not to do in Milkshape, in case you need that: https://hermit-fox.livejournal.com/524.html

(It's the same for animations, but there you also have to take into account timing between set keys and all that. Individual poses only have one set key, while animations often have several)