this is how i created exclusive modes:

FIRST:

void FullscreenOn()
{
 noCursor();

 frame.dispose();  
 frame.setUndecorated( true );  

 GraphicsDevice myGraphicsDevice = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice  ();  
 myGraphicsDevice.setFullScreenWindow( frame );
 if (myGraphicsDevice.isDisplayChangeSupported())
 {  
   DisplayMode myDisplayMode = new DisplayMode(  
   width, height, 32, DisplayMode.REFRESH_RATE_UNKNOWN );  
   myGraphicsDevice.setDisplayMode( myDisplayMode );  
 }
}  


void FullscreenOff()
{  
 GraphicsDevice myGraphicsDevice = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice  ();  
 myGraphicsDevice.setFullScreenWindow( null );  
}



SECOND:

static public void main(String args[])
{  
 PApplet.main(new String[] { "--present", "Attract" });
}



WINDOWED MODE:

static public void main(String args[])
{  
 PApplet.main(new String[] { "--location=-10,-40", "Attract" });
}

void setup()
{
 size( screen.wdith+20, screen.height+40, OPENGL );
 ...
}



any ideas ??

Yes, this has been my experience as well.  Unfortunately, full-screen exclusive mode on a Mac allows for one only monitor to be used (as far as I've been able to tell.) There are some tricks to run something fullscreen on a mac w/o exclusive mode.  It's been discussed here on the forums. I've got some notes about it here too:

http://itp.nyu.edu/varwiki/BigScreens/FullScreenHacks