Foot alignment by positioning???

Hello,
I was wondering if there is a script that takes in a right and left foot of a character, as well as a right and left knee, and constantly aligns the character's foot with the ground, while bending the knees to do so, so that when I move the character (even during edit mode) the character will 'walk', 'run', 'straff', 'kneel' or 'bend' as long as the speed of the movement is 'stretchable', and do nothing IF I move the character too fast. I know IK takes care of that, but my question is more advanced (to fit THIS particular kind of expectation). Thanks.