Restricting FTP access via windows Explorer

[Anil]

You guys may have some trick to do this. I use Group policy to restrict
almost everything. I would like to restrict users to stop using FTP access
from their machine. I used GPO to restrict ftp, http, in connection setting.
That restrict the user from internet explorer or other browser. However, user
can still access using windows explorer and type in address bar like
ftp://servername .com. and this will ask username and password and can easily
access. Is ftp client also built in windows explorer ? If I want to restrict
ftp for those particular users in OU how do i do this ?

Thanks

AT