WinDVD will tell you this under "Configuration".
DVD Info Pro will also do this - despite it looking like it costs, on the left side of their site you can get it for free.
DVD Identifier is also free and will provide this information.
As an aside, if you need to change your machine to read a certain region follow instructions below.
Control Panel -> System. On the left side, click on Device Manager.
In the new Window, typically under DVD/CD-ROM drives right click on your DVD/CD drive and select properties.
The second tab is called DVD Region. You are also normally limited to the number of times you can change it (in the picture below it shows Changes remaining: 5) even if you re-install Windows.