Changing drives icon
First of all copy a icon file to the root of the drive.

example: c:\icon.ico

Then create a file called: autorun.inf in c:\autorun.inf
then open that file and type the following:
[autorun]
icon=icon.ico

save and close the file.
Now open my computer and refresh.. and woh! icon changed....
you can apply to other drives too.
be careful:
"autorun.inf" and "ico.ico" must be in the root of the drive.
example: c:\autorun.inf and c:\icon.ico.
same on the root.

Change thumbnail size

By default, thumbnails are 96x96 pixels in size.
You can change this value for the current user or all users. Current user:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
All users: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer

Go to either key, select Explorer, then create a DWORD value called ThumbnailSize. Double-click it, select Decimal in the Base section, and enter a value between 32 and 256. Restart Windows Explorer