Many of the latest FSX airplanes are lacking a weather radar. I know because of the way FSX weather is programed it is difficult to make a realistic weather radar, still my own view is that it will still be good to have one no matter how accurate it is, just to add to the overall realism of the simulation.
If you are missing a weather radar in your Ifly 737 NG for FSX and you own WX500 package from Reality XP it is possible to add that one in the place of the lower DU. Not the most realistical place in the cockpit, but there isn't much room to place it in another position. If you are using the MAP/EFIS combination of displays, the lower DU is seldomly used anyways.
The instalation is easy.