Archived from groups: microsoft.public.windowsxp.help_and_support (More info?)
Assuming you really mean System Tray, as opposed to Quicklaunch, these
items are typically controlled by the various applications that place
them there, and typically there will be an option in the application's
user interface that you would check/uncheck to include/exclude the
system tray entry. SOMETIMES the option is available merely by
right-clicking on the system tray item itself.