3 times now. I made a thread about changing icons, someone else made a thread, which I answered.
If you already have the .icns files, go to Versiontracker and find "Icns2Rsrc"
Open the .icns file, in Icns2Rsrc.app, and save it as a .Rsrc file. Now the copy/paste method will work, as it will have the icon in the top right, and not an "icns" icon.
The Program, Icns2Rsrc.app comes in a ".sit" file. If you cannot open it, Search Versiontracker for a program called "stuffit expander"
They're both free, and they work.
If one day you wish to make your own icons, Install Apple Developer Tools, from the OS X install disk, or their site. Look for "icon composer" in Developer/applications/utilities/
Drag a custom image into all the fields, and when prompted "Extract Layer mask" and "use scaled version" once filled out, save the .icns file, and begin with the above method.
In the future, as forum searches hardly every work (people don't put good titles for threads, no key words)
use Mroogle, it is macrumors google, it searches not only titles, but all text in a thread -- you should easily find what you need.
Link is in my Signature below: