Why can't I re-add the volume icon to the notification area of my taskbar?

I updated iTunes earlier today, and had to restart my computer, and when I did the taskbar changed. I'm fine with all of the changes, except it removed the volume icon from the notification area, you know down by where the clock and battery icon are. I know how to right click, properties, blah blah blah, but when I see the box to check that says "volume", it's lightened, like how things are when it's not an option to select them. I don't understand why I can't add it back or why it removed it in the first place. Any help here? I'm running with windows vista basic.