@Electroforce
Download 3D Studio Max for free with student license or Blender (free).
Select the windows of the car: windshield, side windows, rear window.
Clone them. Isolate them. Drag n drop a new .dds texture for the internal windows. Convert them to editable poly. Select them all and "flip" them.
Now you have windows with raindrops, once you open the fbx file in Kunos editor and set the shader as "ksWindscreen".
If you like, I can create a video showing you how to do that.
I guarantee you, it's not impossible, if I learned it from zero knowledge of 3D editing