My volume and network icons disappeared and the options to put them back on are

[hotlikesauce.]

greyed out. Does anyone know how to fix this?

[mario583]

INB4RESTARTING!

[CutLess]

Yep, this happens to me, too.  Only on Vista...

As mario583 said, the easiest way to fix that is to restart your computer.

Of course, that's not exactly the best way to fix the problem.  Based on a thread I read in another forum, the problem lies in the fact that Windows essentially saves every single icon in the taskbar (for easy access when the icons are needed).  Over time, the list builds up, and when it gets too full, unwanted stuff starts happening.

The solution is to clear past notifications; a guide to doing that is here.