If you see cars with custom paintjobs, like flames or other pictures, it's often been done Airbrushing. I do it myself, and it's really cool. I airbrush, and paint PC cabinets for friends mostly. I'm currently about to do my PS3, including the handcontrollers and all the cables.
I also paint on canvas or just pieces of wood or metal I can find, just to get practice. It's not a VERY difficult thing, but you'll need to have some sence of how to draw/paint, and you'll need at least one paintgun, and a little air-compressor plus LOTS of time to practice.
If you want to, go to my page and look at my pictures, and I'll upload one I made yesterday :) Look it up on YouTube. There's lots of cool airbrushing to see there :)
An airbrush is a small, air-operated tool that sprays various media including ink and dye. It could also mean altering the picture, like when someone is airbrushed it means they're perfected.