Someone who works on or has built their own car and can fix it when it is broken, knows how it is put together . It is definatly a mind set and not something you can learn. You have to love and understand cars and how they work. I think a hotrodder is like an artist, they can look at an old peice of iron in a field and envision something great.
People who go out and buy a Viper, Mustang or anything that someone else built are car enthusiests, not hotrodders. Not that that is bad, just not the same.
I beleive the term Hotrodder originated from racers who would do whatever it took to squeze every ounce of power out of and engine, sometimes changing the connecting "RODS" to a hotter setup. There are several versions of the theory as to where the term came from.
Just my .02