changing colors

so.. is there any way to easily change the color of a car without having to go through the whole thing with a colorize pen and changing it, and without having to select the whole thing with some kind of lasso tool? i have any program to use. the colorize pen in a pain in the ass, and the lasso tool always misses parts and you have to erase out the parts you don't want colored. i just want to change the color of the car without ruining things like the headlights, windshield, tires.. so on. thanks a bunch.

oops ps i'm mostly using photoimpact but i have photoshop (which i can kind of figure out) and psp (but its version 4 or something silly)

i guess some girl who used to work here did it somehow with vectors if that helps...