When you create the vehicle, go up to it's physics(wya up top on the pop-up in vehicles part) and select human. Make sure you're vehicle has the bones of a human/ I have never tested two legs.With these mod tools it's imposible to make realistic 4 leg walking, but you cna probly do a half ass job by telling it the front right leg is the left leg of a human, and right left leg is the right of a human, and the back legs normal.
We have two leg walking working in MekaKai. We have also gotten walking with the knees in the back, sort of like how dog and cat legs work.
If you cna't getin then add more enter and exit trasitions.