Please review the following:http://www.microsoft.com/en-us/download/details.aspx?id=24373
While Microsoft's Steady State software isn't supported in Win 7, the spreadsheet you can download at this URL describes the local policies you can apply in Win 7 to duplicate its functions.
When you download this spreadsheet, you can see on Row 69 of the SteadyState Reference tab there is a way to hide specific drives from a user or group of users with a local policy.
Lines 14 and 15 on the Instructions Tab should have links to documentation on using policies.
You should be ablle to use the information to hide the drive from any user.
Please let me know if this helps.