If you have Win 7 Ultimate or Pro you coud use Bitlocker, otherwise you'll need software to do this. Truecrypt is free, and Folderblock allows a small amount of encryption free, otherwise around $40 to buy.
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.