
A Google search showed me that this is a fairly common problem, and some of the solutions were not exactly easy... until I found the Taskbar Repair Tool Plus! This little gem (did I mention it's free?) took only a few seconds to download and install, and within 10 seconds my taskbar buttons magically reappeared! Hallelujah!
Now, on a much deeper, more philosophical level... had I not "learned how to learn" I would have had to pay someone to come to my house and fix this minor, but annoying problem. But because I knew what I was looking for, I was able to Google it and find an answer within minutes. This is one example of what it means to be a "lifelong learner" and what we need to be teaching to our students (and other teachers).
Thank you Kelly's Korner! The software will also repair a whole list of other Windows XP problems. http://www.kellys-korner-xp.com/taskbarplus!.htm