Just a quick append to my post. If your only just starting to repaint. DONT try to learn using the default ones.
You'll find it (quite) hard to find all the parts, and then you'll be frustrated when you find a set of parts that use all use the same texture so that when you put text on one part, it appears on a few parts on the plane. (That said, the Extra 300 is one of the better defaults in that respect, you just gotta find everything now ;)
My advice, use the aicraft from here:
www.pmstone.comThey are simple, but not un-realistic, and guess what, each one comes with blank textures for you to work onto, no messing :D
Good luck :D