First thing I'd suggest is download and install Download IconViewer
that way you can look at the icons from the property window there will be an icon tab.
SndVolSSO.dll For volume
pnidui.dll For network
batmeter.dll For the power on a laptop. These are bitmaps.
For a 32-bit system they will be in C:\Windows\System32
For a 64-bit system they will be in both C:\Windows\System32 and C:\Windows\SysWOW64
To properly change a system file you need to take ownership give yourself permission and rename the old file and then copy in the new one look at Post #6 of this thread will tell you how to do it Basic Networking Information
Here is a few tutorials you should look at. Notification Area Icons - Customize Notification Area Icons - Reset Icon Cache - Rebuild