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 resfresh.. and woh! icon changed....
you can apply to other drives too.

be carefull:

"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.