not sure about the weather man on the news.
for the chroma key FX, you can use the presets and play around with the threshold to get desired effect.
or use the color picker and draw a square on the area with the color you want to take out.
You have your clip with your subject videoed against a solid backround.
In MS, find the color of the solid backroud by moving around in the color pallet until the backround turns black. Then place the video you want to fill the black area in the video overlay. I can't remember wether you had to also apply something to the overlaid video without trying it again myself.
I did speaking and moving lips overlay on a photo once.