To set the icon of any drive (hard disk, cd rom or anything else) with a letter (C:\ etc.), run REGEDIT (Start -> Run -> regedit)

Navigate to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer

If one doesn't already exist, create a new KEY called "DriveIcons". Under this key, create a new key with the letter of your drive.

I.e. C for your C:\ drive.

To change the icon for that drive, create a key inside that one called DefaultIcon and set the path of (Default) to the location of your icon

eg C\DefaultIcon\
then (Default) = D:\Documents\C Drive Icon.ico

To change the name of that drive, create a key in the drive letter one (eg C\) called DefaultLabel and set the (Default) to what you want the drive to be called.
This is useful if you want to assign a long name to the floppy drive.