If you're handy enough to install the $1500 Z power steering kit, you're probably handy enough to save $1400 and make your own.
You need an Electric Power Steering Column from following vehicles which are manufactured by Koyo: Saturn Vue - from 2002 to 2007 Chevrolet Equinox - from 2005 to 2007 Saturn Ion - from 2003 to 2006 - only in steering column with metal ECU case.
And this:
http://www.ebay.com/itm/Saturn-Vue-Ion-Chevrolet-Equinox-Electric-power-steering-controller-box-EPAS-/182008071875?vxp=mtr
(ebay seller: brunolopesantunes in case link goes dead)
If you have an aftermarket ecm, megasquirt, etc with a vehicle speed sensor, you can even wire it in to adjust automatically to your settings at speed, if it will output variable resistance.
Sorry, no pics. I have a million things to do to my Z before I worry about electric power steering. But there are plenty of other forums with write ups, and youtube videos demonstrating the concept.
(disclosure: portions of text copied from http://forums.vintage-mustang.com/)