Go regedit and look for this key:
hkey_local_machine\software\microsoft\windows\currentversion\explorer
Now create a new key DriveIcons
Under that key, create a new key of your drive alphabet (eg. "C" for C drive)
Under the C key, create a new key named "DefaultIcon".
Value data in this key will be the location of your icon (eg. C:\Icons\icon a day\Icon-A-Day (Hard Drive).ico)
Refresh your My Computer and there you go