newbie:how to get the frontmost window but a key window

FROM : norio
DATE : Fri Jan 11 05:15:40 2008

Hi,

I'd like to know how to get the most front window below a key window 
(e.g.Find dialog).


I've tried the following things but failed.

1. call currentDocument of the sharedDocumentController and tried to 
get the window from the document.
    But the document returned by currentDocument was nil.

2. call mainWindow of the sharedApplication. But the return object was 
nil.


Thanks in advance.
Norio Ota