If you would like to install Windows Media Center, check out this blog post.
You can download VLC from VideoLan's website. Click the big Download VLC button and to download the installer. When installing use the default options. This registers VLC as a DVD player with Windows.
If the DVD is already inserted, you can open VLC from the start screen to play your DVD. Click Media and then Open Disc. Then press the Play button to play your DVD.