Sorry, Im pretty new to maya...installation:
//
// -copy "ds_ao4maya.mll" to your "..\Alias\MayaXY.0\bin\plug-ins"-folder
// -copy "render_ambientOcclusion.xpm" to your "..\maya\VERSION\prefs\icons"-folder
// -restart maya
// -load the ds_ao4maya.mll (Window -> Settings/Preferences -> Plug-in Manager)
// -you'll find the Ambient Occlusion Node in your Hypershade (under Surface)
//