pacifist, Right click your Taskbar, choose Properties, under the Taskbar tab click the Customize button, under Current Items hilite one at a time each icon and use the dropdown arrow button and choose Always show, click OK/Apply/OK. You may also want to go to the link below and under the letter "N" scroll down to "Notification Area - Icons Disappearing" where you'll find several other possible solutions.
Two icons have disappeared but occasionally reappear for one or two secessions. I believe this happened after the Microsoft updates early November but that may be just a coincidence. The programs are still running when I check in services and I am just wondering why this is happening. The icons that disappeared are Webroot's Spyweeper and Pure Network's, Network Magic, my network manager program.
My system specs are P4 2.8mhz 1024mb ram 160gb hdd running Windows XP Home.