Upper-Lower Animation

Multiple channels of animation, each with a variable blending factor and starting bone, allows for multiple animations to be played simultaneously.

I want to know how to perform Upper body animation while the lower body stays still. For example, in games such as Halo and Counter-Strike, while standing still the player can look around without the feet moving as well (that is until the player looks far enough left or right then the player's feet is then readjusted.)