Finding a .chm help file window

I am launching a .chm help file from my program. I want the program to check to see if the help file is already open. I am trying to use FindWindow() to detect the already-opened window. However, the function always returns 0:

hwnd=FindWindow("","3D World Studio User's Guide")

Does this find it...

Extern "win32"
	Function FindWindowA:Int(nullstring%,WindowText$z)
End Extern
Local handle = FindWindowA(0,"3D World Studio User's Guide")
print handle

?

That did it, thanks.