So if I'm understanding you, you want to use something like Biped's 'planted key' functionality? Where you can lock down a foot and have it not move while you animate the body, right? But then set a 'free key' and have the foot follow the body, right? If so, you're not going to get this sort of behavior with standard max…
I'm currently animating a tarantula for one of my classes. I built a custom rig for it and animation has been going pretty well so far. The image below shows the rig, and how the dummys are linked up. I have one dummy for the main body, as well as one for each appendage. The IKs for the appendages are linked to their own…