cocoa Modal ( using sheet )

[Modal]

// open
[NSApp beginSheet:currentWindow
 modalForWindow:prevWindow
 modalDelegate:self
 didEndSelector:NULL
 contextInfo:NULL];

// close
[NSApp endSheet:currentWindow];
[currentWindow orderOut:nil];

[reference] http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSApplication_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40004004