The PlanePlotter Wiki can be found here :

http://planeplotter.pbwiki.com/

PlanePlotter wiki section on mode-a/c mlat direct link:
http://planeplotter.pbworks.com/w/page/141772821/SQWK%20Mlat%20-%20Mode-AC%20Virtual%20Primary%20Radar%20Network

PlanePlotter main page: (Download section for software updates)
http://www.coaa.co.uk/planeplotter.htm#download

PlanePlotter Online Support page:
http://www.coaa.co.uk/planeplottersupport.htm