I have a simple anti backlash nut for sale on my site http://www.damencnc.com. Anyway feel free to take the idea. If you are in a hurry you can buy it... There are also some design pictures online, i have included one here.
I have tested many setups. i have also tried the auto adjust spring loaded nut, this gave a lot of trouble, the machines was actually able to compress the spring. With increased spring stiffness the nut had a lot of drag..

A friend in the netherlands has also made a nut using compressed air to regulate it. Take a look at http://www.aanrip.nl

I have included a picture

grtz, Kevin