>>>Do you know of any freeware that would let block/unblock access to usb drives?
>>
>>Can I ask why you want to do this?
>
>Coincidentally there is a new article in TechNet WiKi that may help
>
>http://social.technet.microsoft.com/wiki/contents/articles/19993.hiding-custom-set-of-drives-in-the-windows-explorer.aspx

Note: this setting hides drive icons...
In my book such a setting would evoke a false sense of security.