Hello again all!

 I'm so.. SO.. frustrated. I created the start of my animation without IK. It's a long animation, about 500 frames. Everything was fine.. but then the next part of the animation required the feet to stay in place while the figure swayed their thighs/hip side to side slowly.

So I turned on IK for the legs.  Well the feet stayed in place alright, but the animation is all jittery for some reason.. and all I've changed is the Y translation of the hip. The curve looks perfect in the graph editor for the Y translate of the hip element. So I don't see how I could smooth this out... no new keyframes have been created for the legs..

 But anyway.. that's not the main issue. The main issue is that I cannot seem to turn IK back off without completely ruining my previous work. I had read that I could keyframe all of the elements I wanted to remain as is while IK is on.. then turn it off and those elements wouldn't be effected. Well.. the feet flipped in odd directions when I turned IK off, and everything I've tried hasn't helped.

So.. a couple of questions:

1. Anyone know why the legs went jittery? Is this common when animating with IK?  I tried using the side-to-side paramaters on the thighs, but with IK on.. they refuse to move very far at all.

2. Is there no method to switch IK on and off within the same animation I'm working on without it altering my previous work?

3. Is IK worth the trouble at all while animating? I'm starting to think that trying my best to keep the parts I want to stay in place manually via trial and error might be less of a headache than using IK.Sure there's a bit of slide and it takes a lot longer to create.. but I'd rather have a smooth animation.

Oh.. and just in case you want to see the animation.. here's a link. [WARNING: little bit of NUDITY] http://rapidshare.com/files/231646702/LionMG_IK.avi.html

The first part where she bends her knee in is the non IKed part... which I'm happy with. Then hopefully you can make out the jitteryness while her legs sway side to side.

Any and all replies would be MUCH appreciated. Thanks for your time!

This is what I'ld do
Work on the IK-needy animation independently. As in a different file, etc. ONLY work on the IK-needy animation.
Then turn off  the IK.
Then save the result as an animated pose.
Load the original file where you were animating the non-IK animation, and where the other animation should start, just apply the animated pose you saved.

Manoloz's advice is good.  Use the IK sparingly, save as animated pose,
re-insert in a non-IK scene.

The jittering is a common problem.  There are usually two or three possible
solutions to each IK calculation.  One solution may involve (eg) the right knee
bent slightly forward, the other may have the right knee bent slightly backward.
You don't notice the alternate solutions in a still pose, but in an animation
Poser will pick the one that seems closest for each frame.  And the best
solution for frame 10 may have the knee bent backward, then for frame 11 the
knee bent forward, then for 12 backward again.......

Thanks for the replies guys!

I guess there's no way to turn IK off and save my first part of the animation? I very intelligently (NOT >_<) saved the file with IK on.. shooting myself in the foot.