With paint?...
Seriously, the sponsor logos/text are cut vinyl stickers basically. I'd guess the paint is sprayed on and then lacquered with clear to make it very shiny.
Something like the Honda 'earth' scheme was almost entirely decals (I found a pic of it here - you can see the edge of some of the decals peeling). They use very think vinyl which can be stretched around the curves of the car.
Also, a story on it here:
http://www.f1technical.net/features/3758