keep sound when selecting another window

hello everybody,

I have a little problem with vista... The desktop is separated in two screens: my laptop on which I play flight simulator, and another screen just displaying google earth. Google earth is linked to flight simulator via MFSgoogle earth, which is truly great BTW.
The only thing is, when I click on google earth the flight simulator sound shuts down. So is there a way to keep FS sound "always on top"?

thanks for reading this, any comment appreciated.