Silke, there's a preference setting in the actual Library, you can access that by clicking on the "Klingon Toothpick" at the bottom of the library pane. If you expand "General" you'll see a checkbox for "Always on Top". Toggle that off, if the Library is always floating atop PP2010. You'll be able to pop-up the library at any time by clicking on the new "Library pop-up" widget in the upper right hand corner. Then when you hit PP2010 again, the Library is sent to the background. You can also pop-up the library by clicking on it's icon in the OS' tray. I run Win 7, so my tray is in the default position at the bottom of the screen.