To install the cars, just save the texture as bmp and replace the files in the directory:
\CTDPSeasonData\Vehicles\<Team>\2005CTDP_<CAR> (ex: \CTDPSeasonData\Vehicles\McLaren\2005CTDP_MP4-20)
\CTDPSeasonData\Circuits\<COUNTRY>\2005CTDP_<CIRCUIT> (ex: \CTDPSeasonData\Circuits\Australia\2005CTDP_Albert_Park)
For Helmets just make your own helmet according to the Layout and place the bmps into:
Jpeg Compression for Helmets is very high so quality is bad, but you now know how to paint the helmets. The reason behind the bad quality is to avoiding Rip Offs.
But don’t worry. All designs are clean on the textures, you can just paint on the texture and don’t worry, there are no shadings or details you need to do. They are automatically inserted through the game model.
These helmet-textures also work in rFactor.
You’ll find the folder “emaps” included in this templates. There you find a more detailed writeup on emaps and how strong an effect they have in F1C.