The System Tray is full of icons that represent programs that can either be started quickly or are running in the background. Often these icons are added automatically when you install something and your system tray can end up taking up a lot of the task bar. To resolve this you might run a third party utility that moves the icons from the system tray into a separate program area that runs from the system tray. This still leaves all of the programs running but removes some (or most) of them from the actual system tray.
You may find that there are icons in the system tray that you would prefer to delete from there completely because you don't want that particular program running all the time. To do this, first try right clicking on the entry in the system tray to bring up the context menu for that item. Often there is a Close or Exit option at the bottom of the menu that will remove the icon from the system tray for you. Sometimes this is also sufficient to permanently remove the program from the system tray while other times the icon will return the next time that you start Windows.
If there isn't an appropriate option in the context menu or the program comes back the next time you start windows, it is time to check the Startup folder. Right click on the Start button and select Explore from the context menu. Then go into the Programs folder and from there into the Startup folder. If you find an entry here that corresponds to the icon in the system tray then this is what is starting it up. If you delete the entry then the icon should disappear the next time that you start windows.
Note that if you are running Windows NT, 2000, or XP which have individual user profiles then you should also check the Startup folder in the corresponding location under All Users to see if it is being started from there. You may need administrator access to remove the entry in that instance.
If you still haven't found the entry then the next thing to do is to run msconfig (press Start , then Run, then type msconfig and select OK). When the program starts select the Startup tab and check the list of programs that are there. If you find the program you are looking for, remove the check against it and it wont start the next time that you start Windows. Make sure that you don't remove the checks against explorer or systray as these are needed for your system to function.
If you still haven't managed to remove the icon from the system tray then check if there is a related program in the Control Panel. Often system tray entries are started from here (eg. the volume control is activated from the multimedia program). If it is controlled from here then you should find an option in the program in Control Panel to turn it off. Another place to check is the registry. There is a list of registry keys related to starting programs on the Cleaning up Without Reinstalling Windows page. Deleting the entry from the registry should turn it off (but you may want to back up the entries first just in case you delete the wrong thing).
This article written by Stephen Chapman, Felgall Pty Ltd.