After installing Windows XP's Service Pack 2, now none of my running/open applications appear in the taskbar.  I still have the Start Menu and the Quicklaunch and systray icons, but nothing else.  I can still use Alt-Tab switching, but that's it. 

Maybe I shouldn't have installed SP2 yet...I'm assuming that's the cause of the problem...the timing is too much to ignore. 

[edit date='2004-09-21']

So I 'restored' this machine to a previous point, ran and re-ran “sfc /scannow“, and scoured the Internet (and my registry) for a solution, but none of them worked....until I found this link, item 240 on Kelly's Korner's XP tweaks.

Thank you very much to Kelly!

[/edit]