LiSPSM help

i'm am tring to implament Light State Perpective Shadow Map(LiSPSM) and i am having alot of trouble figuring out how to contruct the perpective frustum in light space.  If you know what it is could you awnser some of my questionions.

On the perpective frustum the Y axis is equal to light direction,Z is perpendicular to light direction and X is cross of the Y and Z?

Thats great but that doesn't tell me how to to enclose the view frustum.

I just don't know how to contruct the view frustum for the shadow map.  I guess i don't i just need the location to set the directional light(for those who don't know all lights are directional in LiSPSM)