A little tip if you ever run into the following situation: The Volume Control icon in my Windows XP system tray turned into the same icon as the one for my current anti-virus program of choice, Avast!.
I tried right-clicking and fiddling with both Volume Control (in disguise) and Avast!. Trust me, nothing worked. I let the situation fester for a couple of days. Then I just reached the limit of patience (a heretofore unmeasurably small amount) and went into the Control Panel and started up the Sound and Audio Devices applet. I unchecked the "Place volume icon in the taskbar" and clicked APPLY. Suddenly, I only had one Avast spinning blue ball. Then I re-checked the checkbox and pressed OK.
Problem solved. Itch scratched. Only took three days to think of it.