Start the FSImp xxx installer application and follow the instructions. This should result in the following folder structure
...\X-System ???\Resources\plugins\FSImp.xpl ...\X-System ???\Resources\plugins\FSImp\...

No changes or additions are made to the windows registry.
That was it! Now you should be ready to setup FSImp from within X-Plane.
FSImp plugin for X-Plane