Thanks for your reply, Joe12. This didn't work for me. The Restricted Extras was already installed, and NO media player I downloaded and installed would work. However, a friend of mine found an answer that does work, and in the spirit of Linux, Ubuntu and this site, I'd like to pass it along for others:
Install the libdvdread4 package (no need to add 3rd party repositories) via terminal command line as follows:
sudo apt-get install libdvdread4
It's that simple! Movie Player, pre-installed with Ubuntu 9.10 in my PC, now plays everything!