I'm not sure what do you mean by closewindow dll.
If you try to call Window API function CloseWindow in User32.dll, you'll never be able to close a window. Because the name "CloseWindow" is a little misleading.
This function, CloseWindow, is actually not for close a window, but for minimize a window.
If you haven't try NI's lvwutil.zip, you should give it a try. It has the function you want, and a lot more. You can download it from NI site. It's free.
George Zou
http://gtoolbox.yeah.net
George Zou