Draken 35J 5.1 and 35OE 1.1 are designed for Prepar3D v5 and v4 but are compatible with Flight Simulator X (SP2 and later). Some Prepar3D specific features will not work in FSX, such as the dynamic landing/taxi lights, and the switch sounds in the cockpit. Switch positions will also not be saved between sessions in FSX.
Draken 35J 5.0 and 35OE 1.0 are designed for Prepar3D v4/v5 and will not work properly in earlier versions of Prepar3D or in any version of Microsoft Flight Simulator.
Draken 4.1 requires Microsoft Flight Simulator X SP2 or later. It can be installed in Prepar3D, but it will not work as intended and some major tweaking is needed. You are on your own there.
Draken 3.2 requires Microsoft Flight Simulator 2004 (FS9).