P.S. I keep the iTunes 10 backup folder along with its exe file. So no problem returning.Well actually that thread is a completely different topic. This is where you use an internet connected system to get an updated version of iTunes to install it on a non-internet connected system. As the thread shows there is no issue with this.
And the statement you quoted above is the proof that only 1 version of iTunes can be installed on a computer at one time.
Next up, find a thread where an older iTunes can't read a newer library file, proving the second statement of my response.