You can overlay your videos in Sony Vegas Movie Studio. First drag the picture of TV set in the timeline and drag it to the whole timeline and then place your video above it as showing in the video. Now click on the pan/crop icon and select the picture of TV set. Now resize your window and set your video in the TV set as showing in the video. Now you can play your video but it pops up as the video plays so to fade in your video, you just need to do is to drag the corner of your video as showing in the video to fade in your video and you are done.