These are for Windows and allow AC3D to import and export .ol and .lod files for OpenPlane.
Unzip the file into the plugins folder of your AC3D installation.
http://www.ac3d.org/ac3d/download/OpenPlane.zip
A couple of people have tested these and had success but it appears that most people don't use all of the plugins so if you find any problems, please report them to me.
Andy