Hrm, I tried this problem out on another iMac I have and it doesn't work, just like you guys. One this mac, I can switch the icon no problem. On the other mac, I have to log in as root. One thing that is different, the "paste" is NOT greyed out either mac. The differences between these 2 imacs: this one doesn't have the developer tools installed. The other one does. The other difference: no other user ever changed the HD icon on this machine. On my other iMac, my boyfriend changed under his user account.