If you have enabled Fast User Switch in Windows XP, then every time you switch users back and forth, you will notice an additional ActiveSync icon on your system tray.  If you do this several times in a day, then you will end up having a clutter on the system tray. 

 

  How do I Remove It ?

If you move your mouse over these icons, the dummy icons will disappear leaving behind the genuine one.  Unfortunately, there is no way to completely avoid it unless ofcourse you "Log Off" the active user.  If this is not an option and you find the icons pretty irritating you could consider using a free utility called Resync whenever you want to synchronize.

Resync will close the Wcescomm task, which creates the icons and restarts it so that you have only one (genuine) icon on your task bar.   This should solve your problem about the dummy icon's appearing on your taskbar whenever you switch between logins.