I could imagine this stuff has something to do with Gnome 2 themes...could I be right? I mean, after all when you change a theme it might (but not necessarily) change at least some of the "basic" icons - like Computer, Trash etc. etc...so perhaps you should google for theme-thingies, or visit some gnome-themeing-site?
sorry I can't be of any direct help, but hopefully this guides you to some tracks
I'd bet it's done through some theme-settings, if I was to guess.