Connect external monitor to iMac with full resolution

Hello,

I recently purchased an iMac with a Mini Display port adapter -> DVI, connected to a 24 ".

I have the image problem but as soon as I want to watch a video full screen on the external display is not possible ......

Let me explain with VLC in full screen, it switches me one with the perfect movie full screen, but the second black screen. With Quicktime, can not display the movie in full screen on 24 "this is only possible on the iMac.
With Front Row, full screen on the iMac, screen black on the 24 ..... How to make the video to be displayed in full screen on the 24?
please reply thank you

try here
http://support.apple.com/kb/HT2682

So in VLC, go to Preferences> Video and change many things. First we choose the screen in "full screen video output" and uncheck "black screen" for your second display remains normal.
In Quicktime, also in the Preferences> Full screen, you choose the image on the screen that will host the video in full screen Finally, for Front Row, there is nothing to make your second screen is necessarily black. And to have Front Row on the 2nd screen rather than on the screen of the iMac, you have to say in the preferences pane (in System Preferences) that it is the screen which is 2 main (so that the dock will and the menu bar ...).