Klas,
George is right. FindWindow gets 2 parameters, class and title. If any of the parameters you pass null, everything matches :

FindWindow(Class,Title) && Check both match
FindWindow(0,Title) && Any class match
FindWindow(Class,0) && Any title match
FindWindow(0,0) && Any class and title match

* Fox code
function fWin 
lParameters tuClass, tuWinTitle
DECLARE integer FindWindow in WIN32API string cClass, string cWinName
hWnd = FindWindow(tuClass,tuWintitle)
clear dlls
return hWNd

? fwin("Fox_4000001","Microsoft Visual FoxPro") && 824
? fwin("Fox_4000001",0)                         && 832
? fwin(0,"Microsoft Visual FoxPro")             && 824
? fwin(0,0)                                     && 904

Here interesting thing with only one instance of VFP (development), fwin("Fox_4000001",0) and fwin(0,"Microsoft Visual FoxPro") return different values (where is the main fox window ?). And many VFP window with same title return only first.

I would also test it for you in word if I knew how to write and test that in word.
Cetin