http://bugs.winehq.org/show_bug.cgi?id=23108
--- Comment #1 from Rosanne DiMesio dimesio@earthlink.net 2010-06-10 09:35:49 --- That's not a window, it's an extra, misplaced, taskbar icon. I get it in KDE 3.5.10, too, but I also get an icon in the taskbar that allows me to switch between Powerpoint windows. Are you not getting the regular taskbar icon in KDE 4?
Unchecking "Show all windows in the taskbar" on the Powerpoint Options=>Advanced=>Display menu gets rid of it, but it also gets rid of the ability to switch windows using the normal taskbar icon.
Whether it's on or off, you should still be able to switch windows through View=>Switch Windows. Is that not working for you?