If you have photoshop you can use the pen tool (use 'paths'), trace around whatever you want to be in color then make a layer out of it. Blow it up real big so you can outline the subject well.
then right click 'make selection' 0 feather. right click again and choose 'new>layer via copy' Highlight the layer that has all the stuff you want black and white.
Go to 'image/mode/grayscale' and it will turn the layer black and white, but since your new layer wasn't selected it remains in color.
It's tedious to make really good outlines though, at least it is for me. i can do it but i get lazy
Then again, i'm just assuming that's how she did it, as that's the approach i'd use.
You can also do some neat stuff using this method. do the same thing that's done in the bottom one. outline the people. Then you can take the layer that has everything but the people you want focus on. Add a slight blur, guassian, maybe set it to 1.5. What happens is it adds a very slight blur to the layer, which makes the people you are focusing on appear VERY clear, and pronounced. fun stuff!