First of all congratulations and welcome to Pakwheels and the Belta owners and fan club, post some pictures of your new purchase so that everyone here can have a look see.
My Belta also has the same sensors on it's windshield. The sensors on the windshield are sensors for the toll tags in Japan, your car might have a ETC card reader aswell. The sensors at the toll tags recieve certain signals from the sensors on your cars windshield to see if has the data/amount to pass the toll tag. They're really interesting sensors, too bad they become useless when the car reaches Pakistan.
Your Belta has a Tv/Navigation system but not a Tv/Navigation/DVD system & player. What you can do in order to get the DVD's playing onto the Tv/Navigation screen is to get a 6-12 disc DVD changer, which would go underneath the driver or passenger side seat and a remote sensor which would be attached to your center console corner in order to make the remote work properly. OEM Tv/Navigation systems have certain sockets which make DVD/CD changers compatible. It'll cost you anywhere from PKR: 8,000-15,000 with installation (including the remote aswell).
P.S: Did you get the OEM Toyota Belta owners manual which is in Japanese? If you did get you'll be able to find out what I am talking about.