Abstract: A method of sizing or moving application windows in a windowed operating system environment. The method described allows application windows to be moved or sized without blocking application processing from proceeding in other application windows in the environment. The method comprises the steps of establishing at least one filter between an application window to be sized or moved and the windowed operating system, intercepting messages travelling between the operating system and the application window, processing those messages, and returning a neutral message to the windowed operating system. The neutral message does not require the windowed operating system to take further action, thereby permitting the windowed operating system to proceed with application processing tasks in other windows.