I don't quite understand what you did, but all the windows icons are stored in shell32.dll and moricons.dll for Windows xp.
You might have those dlls the Win 7 versions.
I think it's risky to replace the dll's so, if you have the patience you can change them manually, (at least for desktop, by right click,proprieties, desktop, customize desktop) if you get a copy of the dll files from a xp version and open them. Or with Desktop architect program.