Erm... isn't that the way it should be? That is how my HP laptop works. Effectively the two monitors show a view of one double-sized screen with the icons stacked on the left side.
If I want to use excel on the left screen (laptop) I simply launch the programme. Then if I want Word on the external screen, I launch Word then drag it into the second screen. Then I have both programmes working on separate screens.
If this isn't the way it should work, I would like to know the answer too! :)