For changing the colour make a rough selection with the pen tool (set to path mode then make selection) or the pollygon lassoo tool, then to fine tune your selection get a soft brush and press "q" to go into quick mask mode, and t hen zoom in and make it a nice job.
Once you have selected the aera you want, zoom back out, duplicate the layer (so as to not mod the old one) and then go to "adjustments > colorbalance" and change the colour there.
It ur putting carbon firbre on the body work, set the blend mode to overlay, make a good pattern, and use the liquify tool to get itso it curves with the car.
vanishing point in CS2 is worth looking into for putting wheels on to get the right pespective.
just google search whatever it is that you wanna do and then do all the tutoirlals. Keep doing the tutorials !