Where are the toobar icons located? (ACAD2007/08).
I modified an icon, it was saved to:
 
C:\Documents and Settings\<user name>\Application Data\Autodesk\AutoCAD 2007\R17.0\enu\Support\Icons
 
but the other icons are not there.
 
I could not invoke the new icon either.

Standard (internal) icons are taken from a AutoCAD DLL library.

Thanks, but how can I replace the new edited icon into CUI toolbars?
Can we see the standard icons in the DLL?
Are they BMP or some other raster image format?

You cannot change the icons inside the default DLL file but you can make your own icons - either standalone BMP files or a custom DLL file. You can edit the icons through the CUI editor (CUI command).

Thanks again.
I have edited and created icons (BMP), but cannot find a way to import them into the CUI

In the CUI dialog go to the specific command and in the right pane click on the Edit button below the icon. Then open your BMP, RLE or DIB icon file.