How can I speed up the animation loops for games?

I know how to do that in 3dmax, using time warp in biped mixer.
but I cannot afford 3dmax now, so I starting using Blender 2.5 stable.

I cannot find any answer around web elsewhere.

How can I use “time warp” using Blender 2.57b for animations?

I also using meta-rig.

Thanks.