Microsoft raves about how Media Player plays DVDs. But that's a lie. Windows XP can't play DVDs right out of the box. See, even though you've bought a Windows XP computer, a DVD drive, and a DVD, you need something else: special software called a decoder. This bit of software, called a codec because itconverts one format to another, enables your computer to translate numbers on a disc into videos of galloping horses on the screen.