I was going to call this instructable "Stereo Echo Head Transplant"... here's how I swapped the CD/radio/cassette head unit (head transplant - get it?) from my Toyota Echo with the crappy radio-only head unit from Carla's car.
She had been asking for a new car stereo for a while, problem was that she wanted one with a cassette player as well as a CD player, which turned out to be impossible to find in aftermarket car radios. Since my car stereo actually does have a cassette unit, I decided to give her mine, as a Xmas present. Meaning I'll be stuck with the crappy one for now, but that's easily fixed.
Swapping stereos between two cars of the same year and make is about as easy as it gets - no need to worry about cable harnesses, etc. A good starter project for someone who's never worked on a car stereo before.
Yes, we have matching cars. Ya got a problem with that? Three guesses which one is hers...