The main files to look in to change things like MyCompuer, MyDocuments etc. etc. are imageres.dll and shell32.dll
Files I change icons in are:
AUTHUI.DLL
DDORES.DLL
EXPLORER.EXE
IEFRAME.DLL
IMAGERES.DLL
IMAGESP1.DLL
MSTSC.EXE
OCCACHE.DLL
PNIDUI.DLL
REGEDIT.EXE
SHELL32.DLL
TASKMGR.EXE
WBEMCNTL.DLL
ZIPFLDR.DLL
The easiest program I've found for viewing the icons contained in a system file is MicroAngelo "Librarian". Lets you view all the contained icons at once. Problem in it's paid for, but you can get a trial.
Apart from that, with restorator, if you click on the "Icon" Folder in the left window you can select to extract all the icons to a folder where you can view and decide which icons to change at your leisure.
When you say users, can you post a picture or link to of which one it is??
I've changed that many myself I can't 100% remember but in the imageres.dll file look at icon number 105 for My Computer icon when using Restorator.
EDIT! A very quick way to view what, if any, icons are contained in a system file is to download and install a free program called Link Removed - Invalid URL. This adds a tab under the files Properties window when you select Properties from its Context Menu.