As you haven't got a definite answer yet (even from the redoubtable JohnInKansas) I'll tentatively suggest this: I lost most of the icons in the System Tray (?Notification Area - I'm not too hot on the nomenclature) and Google revealed the suggestion that it's all down to rushing poor old aging XP when it's just getting itself going. When you start up - and maybe it's only specifically if you have a password-protected user - don't attempt to log in until initial start-up activity subsides and the machine is idle (or if your hardware is too good to make that apparent wait at least a minute,) then after log-in don't do anything else until all the icons have appeared. Sounds crazy, but it works for me. I've taken to Hibernating instead of Closing Down when I know that I'll want to get started in a hurry in the morning!

SJ